Investment Securities, Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost [Abstract]
Within one year	$ 66,137
After one year through five years	66,205
After five years through ten years	13,945
After ten years	29,137
Amortized cost, excluding securities without single maturity date	175,424
Investment securities not due at a single maturity date, mortgage-backed securities	272,858
Amortized cost	448,282
Fair/Book Value [Abstract]
Within one year	66,141
After one year through five years	66,115
After five years through ten years	13,788
After ten years	28,948
Fair/Book value, excluding securities without single maturity date	174,992
Investment securities not due at a single maturity date, mortgage-backed securities	273,271
Fair/Book value	448,263	$ 369,137
Book Value [Abstract]
Within one year	1,905
After one year through five years	9,530
After five years through ten years	12,699
After ten years	33,975
Book value, excluding securities without single maturity date	58,109
Investment securities not due at a single maturity date, mortgage-backed securities	0
Book value	58,109	61,396
Fair Value [Abstract]
Within one year	1,907
After one year through five years	9,556
After five years through ten years	12,747
After ten years	34,198
Fair/Book value, excluding securities without single maturity date	58,408
Investment securities not due at a single maturity date, mortgage-backed securities	0
Fair value	$ 58,408	$ 62,388