| **Accumulated Other Comprehensive Income (Loss) (Tables)**   | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
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| **Equity [Abstract]**                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Summary of Changes in Accumulated Other Comprehensive Loss   | Following is a summary of the changes in the accumulated balances of accumulated other comprehensive income (loss), which is presented net of tax, as of December 31, 2016 and 2015: Unrealized Gains and (Losses) on Available-for-Sale SecuritiesAccumulated other comprehensive loss at December 31, 2014$(1,325)Other comprehensive income before reclassifications3,428Amounts reclassified from accumulated other comprehensive loss(2,789)Net current year other comprehensive income639Accumulated other comprehensive loss at December 31, 2015(686)Other comprehensive income before reclassifications3,685Amounts reclassified from accumulated other comprehensive income(492)Net current year other comprehensive income3,193Accumulated other comprehensive income at December 31, 2016$2,507                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Reclassification out of Accumulated Other Comprehensive Loss | The following is a summary of the tax effects allocated to other comprehensive income for the year ended December 31, 2016:  Year Ended December 31, 2016  Before-Tax Amount Tax Benefit or (Expense) Net-of-Tax AmountUnrealized gains and (losses) on investments and restricted investments:      Unrealized gains on available-for-sale investments $5,997 $(2,308) $3,689Unrealized losses on restricted investments (6) 2 (4)Less: reclassification adjustment for gains included in earnings (795) 303 (492)Net unrealized gains 5,196 (2,003) 3,193Other comprehensive income $5,196 $(2,003) $3,193The following is a summary of the tax effects allocated to other comprehensive income for the year ended December 31, 2015:  Year Ended December 31, 2015  Before-Tax Amount Tax Benefit or (Expense) Net-of-Tax AmountUnrealized gains on investments:      Unrealized gains on available-for-sale investments $5,650 $(2,222) $3,428Less: reclassification adjustment for gains included in earnings (5,311) 2,522 (2,789)Net unrealized gains 339 300 639Other comprehensive income $339 $300 $639 |

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| - References
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| - Definition
Tabular disclosure of information about items reclassified out of accumulated other comprehensive income (loss).
+ References
No definition available.
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| - Definition
Tabular disclosure of the components of accumulated other comprehensive income (loss).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669686-108580
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