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, 2017	Dec. 31, 2016
Amortized Cost
Due in one year or less	$ 3,604	$ 2,703
Due after one through five years	10,687	16,359
Due after five through ten years	57,708	60,614
Due after ten years	297,324	281,234
Total debt securities with a single maturity date	369,323	360,910
Total Investment Securities	715,055	696,189
Fair Value
Due in one year or less	3,643	2,717
Due after one through five years	11,260	17,068
Due after five through ten years	59,851	62,241
Due after ten years	299,761	281,763
Total debt securities with a single maturity date	374,515	363,789
Total Investment Securities	730,788	696,862
Amortized Cost
Due in one year or less	4,771	2,046
Due after one through five years	70,442	61,921
Due after five through ten years	51,387	61,606
Due after ten years	127,147	121,857
Total debt securities with a single maturity date	253,747	247,430
Total Investment Securities	596,429	607,643
Fair Value
Due in one year or less	4,825	2,047
Due after one through five years	71,687	63,193
Due after five through ten years	51,438	61,145
Due after ten years	128,049	121,906
Total debt securities with a single maturity date	255,999	248,291
Investment securities held to maturity	602,091	611,933
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
Without single maturity date	323,912	313,459
Fair Value
Without single maturity date	322,699	312,292
Amortized Cost
Without single maturity date	342,682	360,213
Total Investment Securities	342,682	360,213
Fair Value
Without single maturity date	346,092	363,642
Investment securities held to maturity	346,092	363,642
Equity securities
Amortized Cost
Without single maturity date	21,820	21,820
Fair Value
Without single maturity date	33,574	20,781
Amortized Cost
Without single maturity date
Fair Value
Without single maturity date