Investments (Tables)

12 Months Ended

Dec. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Schedule of Investments and Restricted Investments

At 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 Value
Debt Securities:
U.S. Treasury securities	$	184,819	$	—	$	79	$	184,740
Corporate debt securities	7,273		—		981		6,292
Preferred stock	265		—		57		208
	192,357		—		1,117		191,240
Restricted investments:
Guaranteed income fund	7,072		—		—		7,072
	$	199,429	$	—	$	1,117	$	198,312

At December 31, 2014 investments and restricted investments classified as available-for-sale securities were as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Debt Securities:
U.S. Treasury securities	$	509,783	$	32	$	—	$	509,815
Corporate debt securities	101,587		—		1,482		100,105
Preferred stock	26,963		—		5		26,958
	638,333		32		1,487		636,878
Restricted investments:
Guaranteed income fund	7,940		—		—		7,940
	$	646,273	$	32	$	1,487	$	644,818

Continuous Unrealized Loss Position

The Company has revised this disclosure in the following table that provides the corporate debt securities in continuous unrealized loss position and their related fair values:    

	As of December 31, 2015								As of December 31, 2014
	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 Losses
Debt securities:
U.S. Treasury securities	$	184,740	$	79	$	—	$	—	$	109,984	$	6	$	—	$	—
Corporate debt securities	6,292		981		—		—		85,845		1,294		14,260		188
Preferred stock	208		57		—		—		23,683		10		—		—
	$	191,240	$	1,117	$	—	$	—	$	219,512	$	1,310	$	14,260	$	188

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, 2015, 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.

	Cost		Fair Value
Due in one year or less	$	184,819	$	184,740
Due after one year through five years	7,175		6,205
Due after ten through fifteen years	98		87
	192,092		191,032
Preferred stock	265		208
Restricted investments	7,072		7,072
	$	199,429	$	198,312