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, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less - Amortized Cost	$ 3,661	$ 3,127
Due after one through five years - Amortized Cost	13,265	9,565
Due after five through ten years - Amortized Cost	51,070	48,675
Due after ten years - Amortized Cost	222,133	155,679
Total debt securities with a single maturity date - Amortized Cost	290,129	217,046
Total Investment Securities - Amortized Cost	579,152	529,212
Fair Value
Due in one year or less - Fair Value	3,715	3,153
Due after one through five years - Fair Value	13,854	9,840
Due after five through ten years - Fair Value	53,347	50,889
Due after ten years - Fair Value	230,338	164,851
Total debt securities with a single maturity date - Fair Value	301,254	228,733
Total Investment Securities - Fair Value	597,839	549,543
Amortized Cost
Due in one year or less - Amortized Cost	5,521	6,258
Due after one through five years - Amortized Cost	24,076	18,440
Due after five through ten years - Amortized Cost	81,286	85,997
Due after ten years - Amortized Cost	107,911	93,748
Total debt securities with a single maturity date - Amortized Cost	218,794	204,443
Fair Value
Due in one year or less - Fair Value	5,533	6,329
Due after one through five years - Fair Value	25,086	18,930
Due after five through ten years - Fair Value	83,355	87,903
Due after ten years - Fair Value	110,361	96,901
Total debt securities with a single maturity date - Fair Value	224,335	210,063
Investment securities held to maturity - fair value	627,848	647,723
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
Without single maturity date - Amortized Cost	287,317	310,460
Fair Value
Without single maturity date - Fair Value	294,879	319,104
Amortized Cost
Without single maturity date - Amortized Cost	392,160	426,645
Fair Value
Without single maturity date - Fair Value	403,513	437,660
Investment securities held to maturity - fair value	403,513	437,660
Equity securities
Amortized Cost
Without single maturity date - Amortized Cost	1,706	1,706
Fair Value
Without single maturity date - Fair Value	$ 1,706	$ 1,706