| **Investments (Tables)**                               | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
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| **Investments, Debt and Equity Securities [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Schedule of Investments and Restricted Investments     | At December 31, 2016 investments and restricted investments classified as available-for-sale securities were as follows:  Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair ValueInvestments:       Corporate debt securities$135,590 $5,311 $1,769 $139,132Preferred stock36,048 656 111 36,593 171,6385,9671,880175,725Restricted investments:       Short-term bond4,232 — 6 4,226Money market fund1,410 — — 1,410 5,642 — 6 5,636 $177,280 $5,967 $1,886 $181,361At December 31, 2015 investments and restricted investments classified as available-for-sale securities were as follows:  Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair ValueInvestments:       U.S. Treasury securities$184,819 $— $79 $184,740Corporate debt securities7,273 — 981 6,292Preferred stock265 — 57 208 192,357 — 1,117 191,240Restricted investments:       Guaranteed income fund7,072 — — 7,072 $199,429 $— $1,117 $198,312 |
| Continuous Unrealized Loss Position                    | The following table provides the debt securities, preferred stock and restricted investments unrealized loss position and related fair values: As of December 31, 2016 As of December 31, 2015 Less Than 12 Months 12 Months or Greater Less Than 12 Months 12 Months or Greater Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized LossesInvestments:               U.S. Treasury securities$— $— $— $— $184,740 $79 $— $—Corporate debt securities64,516 1,410 6,971 359 6,292 981 — —Preferred stock— — 153 111 208 57 — —Restricted investments:               Short-term bond4,226 6 — — — — — — $68,742 $1,416 $7,124 $470 $191,240 $1,117 $— $—                                                                                                                                                                             |
| Contractual Maturities of Investments                  | The net carrying value and estimated fair value of investments and restricted investments classified as available-for-sale at December 31, 2016, by contractual maturity are shown in the following table.  Actual maturities may differ from contractual maturities because certain borrowers have the right to call or prepay obligations. Amortized Cost Fair ValueDue in one year or less$3,910 $3,719Due after one year through five years131,581 135,344Due after ten through fifteen years99 69 135,590 139,132Preferred stock36,048 36,593Restricted investments5,6425,636 $177,280 $181,361                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |

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| - Definition
Tabular disclosure of fair value of investments in debt and equity securities in an unrealized loss position categorized neither as held-to-maturity nor trading securities.
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No definition available.
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| - Definition
Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.
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| - Definition
Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments.
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