Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available for Sale, Amortized Cost
Due in one year or less	$ 4,658
Due after one through five years	13,725
Due after five through ten years	52,878
Due after ten years	220,600
Amortized Cost	291,861
Total Investment Securities	640,499
Available for Sale, Fair Value
Due in one year or less	4,704
Due after one through five years	14,295
Due after five through ten years	55,375
Due after ten years	231,672
Fair Value	306,046
Total Investment Securities	658,400
Held to Maturity, Amortized Cost
Due in one year or less	4,144
Due after one through five years	28,054
Due after five through ten years	81,483
Due after ten years	106,086
Amortized Cost	219,767
Total Investment Securities	618,599	$ 631,088
Held to Maturity, Fair Value
Due in one year or less	4,148
Due after one through five years	29,175
Due after five through ten years	83,646
Due after ten years	109,765
Fair Value	226,734
Total Investment Securities	632,380	647,723
U.S. Government-sponsored mortgage-backed securities
Available for Sale, Amortized Cost
Without single maturity date	342,550
Available for Sale, Fair Value
Without single maturity date	346,266
Held to Maturity, Amortized Cost
Total Investment Securities	398,832	426,645
Held to Maturity, Fair Value
Total Investment Securities	405,646	$ 437,660
Equity securities
Available for Sale, Amortized Cost
Without single maturity date	3,912
Available for Sale, Fair Value
Without single maturity date	3,912
Certificates of deposit
Available for Sale, Amortized Cost
Without single maturity date	2,176
Available for Sale, Fair Value
Without single maturity date	$ 2,176