Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Amortized Cost
Due in one year or less	$ 2,287	$ 2,703
Due after one through five years	7,944	16,359
Due after five through ten years	70,137	60,614
Due after ten years	286,188	281,234
Total debt securities with a single maturity date	366,556	360,910
Total Investment Securities	718,789	696,189
Fair Value
Due in one year or less	2,288	2,717
Due after one through five years	8,294	17,068
Due after five through ten years	73,381	62,241
Due after ten years	293,744	281,763
Total debt securities with a single maturity date	377,707	363,789
Total Investment Securities	742,759	696,862
Amortized Cost
Due in one year or less	6,111	2,046
Due after one through five years	70,140	61,921
Due after five through ten years	56,851	61,606
Due after ten years	132,641	121,857
Total debt securities with a single maturity date	265,743	247,430
Total Investment Securities	600,564	607,643
Fair Value
Due in one year or less	6,201	2,047
Due after one through five years	71,314	63,193
Due after five through ten years	57,493	61,145
Due after ten years	135,597	121,906
Total debt securities with a single maturity date	270,605	248,291
Investment securities held to maturity	609,256	611,933
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
Without single maturity date	330,413	313,459
Fair Value
Without single maturity date	330,235	312,292
Amortized Cost
Without single maturity date	334,821	360,213
Total Investment Securities	334,821	360,213
Fair Value
Without single maturity date	338,651	363,642
Investment securities held to maturity	338,651	363,642
Equity securities
Amortized Cost
Without single maturity date	21,820	21,820
Fair Value
Without single maturity date	34,817	20,781
Amortized Cost
Without single maturity date
Fair Value
Without single maturity date