Investments - Investments Classified by Contractual Maturity Date (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Amortized Cost
Due in one year or less	$ 2,214
Due after one year through five years	108,727
Due after five years through ten years	22,425
Due after ten years	8,224
Mortgage-backed securities	305,396
Total	446,986	441,562
Estimated Fair Value
Due in one year or less	2,248
Due after one year through five years	110,065
Due after five years through ten years	22,767
Due after ten years	7,824
Mortgage-backed securities	305,145
Total	$ 448,049	$ 434,587