| **Fair Value Measurements - Table 1 (Details) (Restricted Marketable Securities [Member], USD $)In Millions, unless otherwise specified** | 12 Months Ended                                                                                                                                                                                                                                                                                            |
|-------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| Prepaid Expenses and Other Current Assets [Member]                                                                                        |                                                                                                                                                                                                                                                                                                       |   |
| **Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]**                                                             |                                                                                                                                                                                                                                                                                                       |   |
| Available-for-sale Securities, Fair Value                                                                                                 | $ 4.6us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember                                                                                    | $ 4.7us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember |
| Fair Value, Valuation Techniques                                                                                                          | M                                                                                                                                                                                                                                                                                                          | M |
| Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]                                                 |                                                                                                                                                                                                                                                                                                       |   |
| **Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]**                                                             |                                                                                                                                                                                                                                                                                                       |   |
| Available-for-sale Securities, Fair Value                                                                                                 | 0us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember   | 0us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember |
| Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]                                                 |                                                                                                                                                                                                                                                                                                       |   |
| **Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]**                                                             |                                                                                                                                                                                                                                                                                                       |   |
| Available-for-sale Securities, Fair Value                                                                                                 | 4.6us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember | 4.7us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember |
| Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member]                                                 |                                                                                                                                                                                                                                                                                                       |   |
| **Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]**                                                             |                                                                                                                                                                                                                                                                                                       |   |
| Available-for-sale Securities, Fair Value                                                                                                 | 0us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember   | 0us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember |
| Other Long-Term Assets [Member]                                                                                                           |                                                                                                                                                                                                                                                                                                       |   |
| **Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]**                                                             |                                                                                                                                                                                                                                                                                                       |   |
| Available-for-sale Securities, Fair Value                                                                                                 | 45.9us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_OtherNoncurrentAssetsMember/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember                                                                                                    | 42.9us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_OtherNoncurrentAssetsMember/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember |
| Fair Value, Valuation Techniques                                                                                                          | M                                                                                                                                                                                                                                                                                                          | M |
| Other Long-Term Assets [Member] | Fair Value, Inputs, Level 1 [Member]                                                                    |                                                                                                                                                                                                                                                                                                       |   |
| **Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]**                                                             |                                                                                                                                                                                                                                                                                                       |   |
| Available-for-sale Securities, Fair Value                                                                                                 | 0us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_OtherNoncurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember                  | 0us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_OtherNoncurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember |
| Other Long-Term Assets [Member] | Fair Value, Inputs, Level 2 [Member]                                                                    |                                                                                                                                                                                                                                                                                                       |   |
| **Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]**                                                             |                                                                                                                                                                                                                                                                                                       |   |
| Available-for-sale Securities, Fair Value                                                                                                 | 45.9us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_OtherNoncurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember               | 42.9us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_OtherNoncurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember |
| Other Long-Term Assets [Member] | Fair Value, Inputs, Level 3 [Member]                                                                    |                                                                                                                                                                                                                                                                                                       |   |
| **Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]**                                                             |                                                                                                                                                                                                                                                                                                       |   |
| Available-for-sale Securities, Fair Value                                                                                                 | $ 0us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_OtherNoncurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember                | $ 0us-gaap_AvailableForSaleSecurities/ hls_FairValueByBalanceSheetLineItemsAxis= us-gaap_OtherNoncurrentAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ hls_FairValueByFinancialInstrumentAxis= hls_RestrictedMarketableSecuritiesMember |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562
+ Details**Name:**us-gaap_AvailableForSaleSecurities**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Description of the inputs and valuation technique(s) used to measure fair value.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258
+ Details**Name:**us-gaap_FairValueMeasurementsValuationTechniques**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |