Investments - Investments Classified by Contractual Maturity Date (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Amortized Cost
Due in one year or less	$ 887
Due after one year through five years	107,842
Due after five years through ten years	20,512
Due after ten years	13,698
Mortgage-backed securities	298,623
Total	441,562	627,462
Estimated Fair Value
Due in one year or less	893
Due after one year through five years	108,582
Due after five years through ten years	20,387
Due after ten years	12,611
Mortgage-backed securities	292,114
Total	$ 434,587	$ 640,212