Securities Available-for-Sale - Summary of Securities Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 495,931	$ 1,414,595
Gross Unrealized Gains	1,217	21,477
Gross Unrealized Losses	2,247	1,271
Total, Fair Value	494,901	1,434,801
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,997	2,000
Gross Unrealized Gains		4
Gross Unrealized Losses	1
Total, Fair Value	1,996	2,004
U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	9,995	130,048
Gross Unrealized Gains	3	360
Gross Unrealized Losses		68
Total, Fair Value	9,998	130,340
SBA Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,414	8,043
Gross Unrealized Gains	17	113
Gross Unrealized Losses
Total, Fair Value	7,431	8,156
U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	429,665	1,212,953
Gross Unrealized Gains	1,032	20,816
Gross Unrealized Losses	1,388	412
Total, Fair Value	429,309	1,233,357
Privately Issued Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,434	2,938
Gross Unrealized Gains	6	31
Gross Unrealized Losses	22	22
Total, Fair Value	2,418	2,947
Obligations Issued by States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	41,720	55,855
Gross Unrealized Gains	18	41
Gross Unrealized Losses	725	722
Total, Fair Value	41,013	55,174
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,300	2,300
Gross Unrealized Gains
Gross Unrealized Losses	111	47
Total, Fair Value	2,189	2,253
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	406	458
Gross Unrealized Gains	141	112
Gross Unrealized Losses
Total, Fair Value	$ 547	$ 570