Investment Securities - Contractual Maturities of Debt Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Due in one year, Amortized Cost	$ 147,705
Due after one year through five years, Amortized Cost	41,978
Due after five years through ten years, Amortized Cost	238,461
Due after ten years, Amortized Cost	369,462
Residential mortgage-backed securities, Amortized Cost	969,341
Total investment securities held to maturity, Amortized Cost	1,766,947	1,599,707
Due in one year, Fair Value	148,150
Due after one year through five years, Fair Value	46,652
Due after five years through ten years, Fair Value	250,285
Due after ten years, Fair Value	355,519
Residential mortgage-backed securities, Fair Value	963,575
Fair Value	$ 1,764,181	$ 1,657,950