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, 2015	Dec. 31, 2014
Amortized Cost
Due in one year or less - Amortized Cost	$ 3,174	$ 3,127
Due after one through five years - Amortized Cost	10,633	9,565
Due after five through ten years - Amortized Cost	51,968	48,675
Due after ten years - Amortized Cost	216,321	155,679
Total debt securities with a single maturity date - Amortized Cost	282,096	217,046
Total Investment Securities - Amortized Cost	562,589	529,212
Fair Value
Due in one year or less - Fair Value	3,222	3,153
Due after one through five years - Fair Value	11,031	9,840
Due after five through ten years - Fair Value	53,927	50,889
Due after ten years - Fair Value	220,585	164,851
Total debt securities with a single maturity date - Fair Value	288,765	228,733
Total Investment Securities - Fair Value	575,415	549,543
Amortized Cost
Due in one year or less - Amortized Cost	7,831	6,258
Due after one through five years - Amortized Cost	17,813	18,440
Due after five through ten years - Amortized Cost	82,412	85,997
Due after ten years - Amortized Cost	115,559	93,748
Total debt securities with a single maturity date - Amortized Cost	223,615	204,443
Fair Value
Due in one year or less - Fair Value	7,858	6,329
Due after one through five years - Fair Value	18,440	18,930
Due after five through ten years - Fair Value	84,331	87,903
Due after ten years - Fair Value	115,771	96,901
Total debt securities with a single maturity date - Fair Value	226,400	210,063
Investment securities held to maturity - fair value	647,810	647,723
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
Without single maturity date - Amortized Cost	278,787	310,460
Fair Value
Without single maturity date - Fair Value	284,944	319,104
Amortized Cost
Without single maturity date - Amortized Cost	413,486	426,645
Fair Value
Without single maturity date - Fair Value	421,410	437,660
Investment securities held to maturity - fair value	421,410	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