Investments - Schedule of Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 223,036	$ 199,429
Gross Unrealized Gains	275	0
Gross Unrealized Losses	1,388	1,117
Fair Value	221,923	198,312
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	174,367	184,819
Gross Unrealized Gains	197	0
Gross Unrealized Losses	0	79
Fair Value	174,564	184,740
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,086	7,273
Gross Unrealized Gains	78	0
Gross Unrealized Losses	1,152	981
Fair Value	19,012	6,292
Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,930	265
Gross Unrealized Gains	0	0
Gross Unrealized Losses	236	57
Fair Value	22,694	208
Debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	217,383	192,357
Gross Unrealized Gains	275	0
Gross Unrealized Losses	1,388	1,117
Fair Value	216,270	191,240
Money market fund
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,653
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 5,653
Guaranteed income fund
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		7,072
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		$ 7,072

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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-Publisher FASB
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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