Investments - Contractual Maturities of Investments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Cost
Due in one year or less	$ 224,826
Due after one year through five years	56,244
Amortized Cost	281,070
Preferred stock	3,270
Cost	284,340	149,097
Fair Value
Due in one year or less	224,842
Due after one year through five years	53,575
Fair Value	278,417
Preferred stock	3,373
Fair Value	$ 281,790	$ 146,972