Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Available for Sale
Due in one year or less - Amortized Cost	$ 8,404
Due after one through five years - Amortized Cost	11,972
Due after five through ten years - Amortized Cost	57,708
Due after ten years - Amortized Cost	132,704
Total debt securities with a single maturity date - Amortized Cost	210,788
Total Investment Securities - Amortized Cost	610,181
Due in one year or less - Fair Value	8,591
Due after one through five years - Fair Value	12,481
Due after five through ten years - Fair Value	59,110
Due after ten years - Fair Value	126,284
Total debt securities with a single maturity date - Fair Value	206,466
Total Investment Securities - Fair Value	606,341
Held to Maturity
Due in one year or less - Amortized Cost	1,060
Due after one through five years - Amortized Cost	13,116
Due after five through ten years - Amortized Cost	59,473
Due after ten years - Amortized Cost	42,147
Total debt securities with a single maturity date - Amortized Cost	115,796
Total Investment Securities - Amortized Cost	307,794	361,020
Due in one year or less - Fair Value	1,061
Due after one through five years - Fair Value	13,324
Due after five through ten years - Fair Value	59,634
Due after ten years - Fair Value	42,269
Total debt securities with a single maturity date - Fair Value	116,288
Investment securities held to maturity - fair value	314,383	378,174
U.S. Government-sponsored mortgage-backed securities
Available for Sale
Without single maturity date - Amortized Cost	397,687
Without single maturity date - Fair Value	398,169
Held to Maturity
Without single maturity date - Amortized Cost	191,998
Total Investment Securities - Amortized Cost	191,998	243,793
Without single maturity date - Fair Value	198,095
Investment securities held to maturity - fair value	198,095	255,459
Equity securities
Available for Sale
Without single maturity date - Amortized Cost	1,706
Without single maturity date - Fair Value	$ 1,706