Investments Schedule of Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Preferred stock	$ 13,724
Amortized Cost	599,494	149,097
Gross Unrealized Gains	346	88
Gross Unrealized Losses	3,826	2,213
Fair Value	596,014	146,972
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	484,771	124,861
Gross Unrealized Gains	135	88
Gross Unrealized Losses	0	0
Fair Value	484,906	124,949
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	101,210	24,236
Gross Unrealized Gains	0	0
Gross Unrealized Losses	3,826	2,213
Fair Value	97,384	22,023
Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,513
Gross Unrealized Gains	211
Gross Unrealized Losses	0
Fair Value	$ 13,724