Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Amortized Cost
Due in one year or less - Amortized Cost	$ 3,963	$ 4,658
Due after one through five years - Amortized Cost	17,175	13,725
Due after five through ten years - Amortized Cost	54,387	52,878
Due after ten years - Amortized Cost	237,122	220,600
Total debt securities with a single maturity date - Amortized Cost	312,647	291,861
Total Investment Securities - Amortized Cost	611,972	640,499
Fair Value
Due in one year or less - Fair Value	3,990	4,704
Due after one through five years - Fair Value	18,087	14,295
Due after five through ten years - Fair Value	57,310	55,375
Due after ten years - Fair Value	250,867	231,672
Total debt securities with a single maturity date - Fair Value	330,254	306,046
Total Investment Securities - Fair Value	636,785	658,400
Amortized Cost
Due in one year or less - Amortized Cost	2,533	4,144
Due after one through five years - Amortized Cost	32,527	28,054
Due after five through ten years - Amortized Cost	90,434	81,483
Due after ten years - Amortized Cost	106,858	106,086
Total debt securities with a single maturity date - Amortized Cost	232,352	219,767
Fair Value
Due in one year or less - Fair Value	2,541	4,148
Due after one through five years - Fair Value	34,282	29,175
Due after five through ten years - Fair Value	92,992	83,646
Due after ten years - Fair Value	111,754	109,765
Total debt securities with a single maturity date - Fair Value	241,569	226,734
Investment securities held to maturity - fair value	655,445	632,380
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
Without single maturity date - Amortized Cost	295,443	342,550
Fair Value
Without single maturity date - Fair Value	302,586	346,266
Amortized Cost
Without single maturity date - Amortized Cost	401,640	398,832
Fair Value
Without single maturity date - Fair Value	413,876	405,646
Investment securities held to maturity - fair value	413,876	405,646
Equity securities
Amortized Cost
Without single maturity date - Amortized Cost	3,882	3,912
Fair Value
Without single maturity date - Fair Value	$ 3,945	$ 3,912
Amortized Cost
Without single maturity date - Amortized Cost
Fair Value
Without single maturity date - Fair Value
Certificates of deposit
Amortized Cost
Without single maturity date - Amortized Cost		$ 2,176
Fair Value
Without single maturity date - Fair Value		$ 2,176
Amortized Cost
Without single maturity date - Amortized Cost
Fair Value
Without single maturity date - Fair Value