Securities Available-for-Sale (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Summary of Securities Available-for-Sale
Amortized cost	$ 1,414,595	$ 1,244,972
Gross Unrealized Gains	21,477	16,842
Gross Unrealized Losses	1,271	3,138
Total, Fair Value	1,434,801	1,258,676
U.S. Treasury [Member]
Summary of Securities Available-for-Sale
Amortized cost	2,000	1,999
Gross Unrealized Gains	4	13
Total, Fair Value	2,004	2,012
U.S. Government Sponsored Enterprises [Member]
Summary of Securities Available-for-Sale
Amortized cost	130,048	174,657
Gross Unrealized Gains	360	311
Gross Unrealized Losses	68	11
Total, Fair Value	130,340	174,957
SBA Backed Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	8,043	8,714
Gross Unrealized Gains	113	87
Total, Fair Value	8,156	8,801
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	1,212,953	1,020,752
Gross Unrealized Gains	20,816	16,262
Gross Unrealized Losses	412	1,176
Total, Fair Value	1,233,357	1,035,838
Privately Issued Residential Mortgage-Backed Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	2,938	3,509
Gross Unrealized Gains	31
Gross Unrealized Losses	22	311
Total, Fair Value	2,947	3,198
Obligations Issued by States and Political Subdivisions [Member]
Summary of Securities Available-for-Sale
Amortized cost	55,855	21,515
Gross Unrealized Gains	41	84
Gross Unrealized Losses	722	957
Total, Fair Value	55,174	20,642
Other Debt Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	2,300	13,293
Gross Unrealized Losses	47	683
Total, Fair Value	2,253	12,610
Equity Securities [Member]
Summary of Securities Available-for-Sale
Amortized cost	458	533
Gross Unrealized Gains	112	85
Total, Fair Value	$ 570	$ 618