Investments - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Available for sale, Amortized Cost
Due in one year or less	$ 3,944
Due after one year through five years	114,914
Due after five years through ten years	9,846
Due after ten years	2,900
Mortgage-backed securities	270,785
Amortized Cost	402,389
Available for sale, Estimated Fair Value
Due in one year or less	3,985
Due after one year through five years	116,179
Due after five years through ten years	10,243
Due after ten years	2,620
Mortgage-backed securities	271,901
Available for sale, fair value	404,928
Held to maturity, Amortized Cost
Due in one year or less	0
Due after one year through five years	1,177
Due after five years through ten years	10,172
Due after ten years	3,517
Mortgage-backed securities	30,107
Amortized Cost	44,973	$ 45,985
Held to maturity, Estimated Fair Value
Due in one year or less	0
Due after one year through five years	1,166
Due after five years through ten years	9,896
Due after ten years	3,344
Mortgage-backed securities	29,729
Held to maturity, fair value	$ 44,135