Investments - Schedule of Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 174,831	$ 177,280
Gross Unrealized Gain	6,995	5,967
Gross Unrealized Loss	1,755	1,886
Fair Value	180,071	181,361
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	128,200	135,590
Gross Unrealized Gain	6,005	5,311
Gross Unrealized Loss	1,420	1,769
Fair Value	132,785	139,132
Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,525	36,048
Gross Unrealized Gain	876	656
Gross Unrealized Loss	335	111
Fair Value	41,066	36,593
Common Stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,662
Gross Unrealized Gain	110
Gross Unrealized Loss	0
Fair Value	1,772
Debt and Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	170,387	171,638
Gross Unrealized Gain	6,991	5,967
Gross Unrealized Loss	1,755	1,880
Fair Value	175,623	175,725
Short-term bond
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,235	4,232
Gross Unrealized Gain	4	0
Gross Unrealized Loss	0	6
Fair Value	4,239	4,226
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	209	1,410
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	209	1,410
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,444	5,642
Gross Unrealized Gain	4	0
Gross Unrealized Loss	0	6
Fair Value	$ 4,448	$ 5,636