Investment Securities, Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Amortized Cost [Abstract]
Within one year	$ 100,999
After one year through five years	68,610
After five years through ten years	0
After ten years	0
Amortized cost, excluding investment securities not due at a single maturity date	169,609
Investment securities not due at a single maturity date, mortgage-backed securities	183,268
Amortized cost	352,877
Fair/Book Value [Abstract]
Within one year	100,998
After one year through five years	68,986
After five years through ten years	0
After ten years	0
Fair/Book value, excluding investment securities not due at a single maturity date	169,984
Investment securities not due at a single maturity date, mortgage-backed securities	188,873
Fair/Book value	358,857	$ 369,137	$ 344,728
Book Value [Abstract]
Within one year	1,211
After one year through five years	10,906
After five years through ten years	11,644
After ten years	35,144
Book value, excluding investment securities not due at a single maturity date	58,905
Investment securities not due at a single maturity date, mortgage-backed securities	0
Book value	58,905	61,396	66,257
Fair Value [Abstract]
Within one year	1,213
After one year through five years	10,943
After five years through ten years	11,878
After ten years	36,420
Fair value, excluding investment securities not due at a single maturity date	60,454
Investment securities not due at a single maturity date, mortgage-backed securities	0
Fair value	$ 60,454	$ 62,388	$ 66,889