Securities - Held to Maturity with Unrealized Losses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	$ 983,077	$ 87,852
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	24,747	259
Held to maturity securities, Losses 12 months or longer, Fair value	282,108	54,445
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	1,181	682
Held to maturity securities, Total, Fair value	1,265,185	142,297
Held to maturity securities, Total, Gross Unrealized Losses	25,928	941
Municipal obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	115,901
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	5,252
Held to maturity securities, Losses 12 months or longer, Fair value	1,253
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	39
Held to maturity securities, Total, Fair value	117,154
Held to maturity securities, Total, Gross Unrealized Losses	5,291
Mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	147,019
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	2,118
Held to maturity securities, Total, Fair value	147,019
Held to maturity securities, Total, Gross Unrealized Losses	2,118
Collateralized mortgage obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, Losses less than 12 months, Fair Value	720,157	87,852
Held to maturity securities, Losses Less than 12 months, Gross Unrealized Losses	17,377	259
Held to maturity securities, Losses 12 months or longer, Fair value	280,855	54,445
Held to maturity securities, Losses 12 months or longer, Gross Unrealized Losses	1,142	682
Held to maturity securities, Total, Fair value	1,001,012	142,297
Held to maturity securities, Total, Gross Unrealized Losses	$ 18,519	$ 941