Investments - Schedule of Investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 149,097
Gross Unrealized Gains	88
Gross Unrealized Losses	2,213
Fair Value	146,972
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Cost	124,861
Gross Unrealized Gains	88
Gross Unrealized Losses	0
Fair Value	124,949
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cost	24,236
Gross Unrealized Gains	0
Gross Unrealized Losses	2,213
Fair Value	$ 22,023