Summary of Contractual Maturity Information for Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Due in 1 year or less, Amortized Cost	$ 466,001
Due after 1 year through 5 years, Amortized Cost	2,299,824
Due after 5 years through 10 years, Amortized Cost	687,956
Due after 10 years, Amortized Cost	120,593
Total, Amortized Cost	3,574,374
Mortgage-backed securities, Amortized Cost	3,182,642
Securities available for sale, Amortized Cost	6,757,016	6,814,712
Due in 1 year or less, Fair Value	467,789
Due after 1 year through 5 years, Fair Value	2,311,028
Due after 5 years through 10 years, Fair Value	696,024
Due after 10 years, Fair Value	118,589
Total, Fair Value	3,593,430
Mortgage-backed securities, Fair Value	3,166,373
Total securities available for sale, Fair Value	$ 6,759,803	$ 6,762,411