Summary of Contractual Maturity Information for Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Due in 1 year or less, Amortized Cost	$ 931,783
Due after 1 year through 5 years, Amortized Cost	1,118,929
Due after 5 years through 10 years, Amortized Cost	861,965
Due after 10 years, Amortized Cost	208,817
Total, Amortized Cost	3,121,494
Mortgage-backed securities, Amortized Cost	3,553,661
Securities available for sale, Amortized Cost	6,675,155	$ 6,813,011
Due in 1 year or less, Fair Value	932,836
Due after 1 year through 5 years, Fair Value	1,136,979
Due after 5 years through 10 years, Fair Value	887,760
Due after 10 years, Fair Value	213,429
Total, Fair Value	3,171,004
Mortgage-backed securities, Fair Value	3,600,175
Total securities available for sale, Fair Value	$ 6,771,179	$ 6,806,949