Investments - Schedule of Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 173,972	$ 177,280
Gross Unrealized Gain	1,733	5,967
Gross Unrealized Loss	3,494	1,886
Fair Value	172,211	181,361
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,930
Gross Unrealized Gain	0
Gross Unrealized Loss	7
Fair Value	24,923
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	97,563	135,590
Gross Unrealized Gain	713	5,311
Gross Unrealized Loss	2,257	1,769
Fair Value	96,019	139,132
Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,525	36,048
Gross Unrealized Gain	855	656
Gross Unrealized Loss	1,103	111
Fair Value	40,277	36,593
Common stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,481
Gross Unrealized Gain	165
Gross Unrealized Loss	123
Fair Value	6,523
Debt and equity investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	169,499	171,638
Gross Unrealized Gain	1,733	5,967
Gross Unrealized Loss	3,490	1,880
Fair Value	167,742	175,725
Short-term bond
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,254	4,232
Gross Unrealized Gain	0	0
Gross Unrealized Loss	4	6
Fair Value	4,250	4,226
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	219	1,410
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	219	1,410
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,473	5,642
Gross Unrealized Gain	0	0
Gross Unrealized Loss	4	6
Fair Value	$ 4,469	$ 5,636