Securities - Amortized Cost and Fair Value of Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	$ 1,435,823	$ 1,986,882
Securities available for sale, Gross Unrealized Gains	30,191	61,599
Securities available for sale, Gross Unrealized Losses	7,894	39
Securities Available for Sale, Fair Value	1,458,120	2,048,442
US Treasury and government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	615	18,246
Securities available for sale, Gross Unrealized Gains	6	19
Securities available for sale, Gross Unrealized Losses	1
Securities Available for Sale, Fair Value	620	18,265
Municipal obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	43,573	49,608
Securities available for sale, Gross Unrealized Gains	197	571
Securities available for sale, Gross Unrealized Losses	122	14
Securities Available for Sale, Fair Value	43,648	50,165
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	1,337,251	1,715,524
Securities available for sale, Gross Unrealized Gains	29,214	58,903
Securities available for sale, Gross Unrealized Losses	6,495	21
Securities Available for Sale, Fair Value	1,359,970	1,774,406
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	46,288	196,723
Securities available for sale, Gross Unrealized Gains		1,354
Securities available for sale, Gross Unrealized Losses	1,256
Securities Available for Sale, Fair Value	45,032	198,077
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	3,500	2,250
Securities Available for Sale, Fair Value	3,500	2,250
Other equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	4,596	4,531
Securities available for sale, Gross Unrealized Gains	774	752
Securities available for sale, Gross Unrealized Losses	20	4
Securities Available for Sale, Fair Value	$ 5,350	$ 5,279