Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Investment Securities [Line Items]
Due within 1 year, Amortized Cost	$ 33,080
Due after 1 but within 5 years, Amortized Cost	234,971
Due after 5 but within 10 years, Amortized Cost	0
Due after 10 years, Amortized Cost	48,733
Debt securities gross, Amortized Cost	316,784
Amortized Cost	1,350,466		1,169,613
Total debt securities, Amortized Cost	1,349,046
Due within 1 year, Estimated Fair Value	33,141
Due after 1 but within 5 years, Estimated Fair Value	233,065
Due after 5 but within 10 years, Estimated Fair Value	0
Due after 10 years, Estimated Fair Value	30,543
Debt securities gross, Estimated Fair Value	296,749
Fair Value	1,318,365		1,171,303
Total debt securities, Estimated Fair Value	1,316,945
Mortgage-Backed Securities [Member]
Investment Securities [Line Items]
Amortized Cost	1,032,262	[1]
Fair Value	$ 1,020,196	[1]

[1] Mortgage Backed Securities include an amortized cost of $22.6 million and a fair value of $25.2 million for Obligations of U.S. Government agencies issued by Ginnie Mae and Obligations of U.S. Government-sponsored enterprises issued by Fannie Mae and Freddie Mac which had an amortized cost of $1,009.6 million and a fair value of $995.0 million.