Investment Securities, Contract Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Amortized Cost [Abstract]
Within one year	$ 60,504
After one year through five years	68,734
After five years through ten years	0
After ten years	0
Amortized cost, excluding investment securities not due at a single maturity date	129,238
Investment securities not due at a single maturity date, mortgage-backed securities	207,021
Amortized cost	336,259
Fair/Book Value [Abstract]
Within one year	60,503
After one year through five years	69,141
After five years through ten years	0
After ten years	0
Fair/Book value, excluding investment securities not due at a single maturity date	129,644
Investment securities not due at a single maturity date, mortgage-backed securities	212,127
Fair/Book value	341,771	$ 369,137	$ 365,184
Book Value [Abstract]
Within one year	225
After one year through five years	12,034
After five years through ten years	11,425
After ten years	37,851
Book value, excluding investment securities not due at a single maturity date	61,535
Investment securities not due at a single maturity date, mortgage-backed securities	0
Book value	61,535	61,396	63,463
Fair Value [Abstract]
Within one year	225
After one year through five years	12,087
After five years through ten years	11,615
After ten years	38,965
Fair value, excluding investment securities not due at a single maturity date	62,892
Investment securities not due at a single maturity date, mortgage-backed securities	0
Fair value	$ 62,892	$ 62,388	$ 64,218