Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Amortized Cost
Due in one year or less	$ 2,336	$ 4,658
Due after one through five years	22,195	13,725
Due after five through ten years	66,314	52,878
Due after ten years	257,843	220,600
Total debt securities with a single maturity date	348,688	291,861
Total Investment Securities	648,261	640,499
Fair Value
Due in one year or less	2,353	4,704
Due after one through five years	23,463	14,295
Due after five through ten years	70,278	55,375
Due after ten years	273,123	231,672
Total debt securities with a single maturity date	369,217	306,046
Total Investment Securities	675,813	658,400
Amortized Cost
Due in one year or less	2,512	4,144
Due after one through five years	53,530	28,054
Due after five through ten years	76,023	81,483
Due after ten years	107,291	106,086
Total debt securities with a single maturity date	239,356	219,767
Total Investment Securities	624,615	618,599
Fair Value
Due in one year or less	2,533	4,148
Due after one through five years	55,764	29,175
Due after five through ten years	77,338	83,646
Due after ten years	113,348	109,765
Total debt securities with a single maturity date	248,983	226,734
Investment securities held to maturity	647,046	632,380
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
Without single maturity date	297,557	342,550
Fair Value
Without single maturity date	304,580	346,266
Amortized Cost
Without single maturity date	385,259	398,832
Total Investment Securities	385,259	398,832
Fair Value
Without single maturity date	398,063	405,646
Investment securities held to maturity	398,063	405,646
Equity securities
Amortized Cost
Without single maturity date	2,016	3,912
Fair Value
Without single maturity date	2,016	3,912
Amortized Cost
Without single maturity date
Fair Value
Without single maturity date
Certificates of deposit
Amortized Cost
Without single maturity date		2,176
Fair Value
Without single maturity date		2,176
Amortized Cost
Without single maturity date
Fair Value
Without single maturity date