Securities Available-for-Sale (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of Securities Available-for-Sale
Amortized cost	$ 1,392,193	$ 1,414,595
Gross Unrealized Gains	17,598	21,477
Gross Unrealized Losses	2,531	1,271
Total, Fair Value	1,407,260	1,434,801
U.S. Treasury [Member]
Summary of Securities Available-for-Sale
Amortized cost	2,000	2,000
Gross Unrealized Gains	1	4
Gross Unrealized Losses
Total, Fair Value	2,001	2,004
U.S. Government Sponsored Enterprises [Member]
Summary of Securities Available-for-Sale
Amortized cost	174,986	130,048
Gross Unrealized Gains	346	360
Gross Unrealized Losses	117	68
Total, Fair Value	175,215	130,340
Small Business Administration [Member]
Summary of Securities Available-for-Sale
Amortized cost	7,906	8,043
Gross Unrealized Gains	108	113
Gross Unrealized Losses
Total, Fair Value	8,014	8,156
U.S. Government Agency and Sponsored Enterprise Mortgage Backed Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	1,149,692	1,212,953
Gross Unrealized Gains	16,957	20,816
Gross Unrealized Losses	1,613	412
Total, Fair Value	1,165,036	1,233,357
Privately Issued Residential Mortgage Backed Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	2,805	2,938
Gross Unrealized Gains	31	31
Gross Unrealized Losses	16	22
Total, Fair Value	2,820	2,947
Obligations Issued by States and Political Subdivisions [Member]
Summary of Securities Available-for-Sale
Amortized cost	52,046	55,855
Gross Unrealized Gains	30	41
Gross Unrealized Losses	723	722
Total, Fair Value	51,353	55,174
Other Debt Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	2,300	2,300
Gross Unrealized Gains
Gross Unrealized Losses	62	47
Total, Fair Value	2,238	2,253
Equity Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	458	458
Gross Unrealized Gains	125	112
Gross Unrealized Losses
Total, Fair Value	$ 583	$ 570