Summary of Contractual Maturity Information for Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investments Debt And Equity Securities [Abstract]
Due in 1 year or less, Amortized Cost	$ 406,525
Due after 1 year through 5 years, Amortized Cost	2,249,226
Due after 5 years through 10 years, Amortized Cost	705,537
Due after 10 years, Amortized Cost	131,982
Total, Amortized Cost	3,493,270
Mortgage-backed securities, Amortized Cost	3,180,331
Total securities available for sale, Amortized Cost	6,673,601	6,814,712
Due in 1 year or less, Fair Value	408,703
Due after 1 year through 5 years, Fair Value	2,263,974
Due after 5 years through 10 years, Fair Value	711,189
Due after 10 years, Fair Value	128,552
Total, Fair Value	3,512,418
Mortgage-backed securities, Fair Value	3,188,205
Total securities available for sale, Fair Value	$ 6,700,623	$ 6,762,411