Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Investment Securities [Line Items]
Due within 1 year, Amortized Cost		$ 3,300
Due after 1 but within 5 years, Amortized Cost		17,397
Due after 5 but within 10 years, Amortized Cost		27,075
Due after 10 years, Amortized Cost		41,895
Debt securities gross, Amortized Cost		89,667
Amortized Cost		790,082	$ 891,111
Total debt securities, Amortized Cost		788,412
Due within 1 year, Estimated Fair Value		3,292
Due after 1 but within 5 years, Estimated Fair Value		17,343
Due after 5 but within 10 years, Estimated Fair Value		27,229
Due after 10 years, Estimated Fair Value		35,607
Debt securities gross, Estimated Fair Value		83,471
Estimated Fair Value of Available for Sale		778,612	$ 886,560
Total debt securities, Estimated Fair Value		776,942
Mortgage-Backed Securities [Member]
Investment Securities [Line Items]
Amortized Cost	[1]	698,745
Estimated Fair Value of Available for Sale	[1]	$ 693,471

[1] Mortgage Backed Securities include an amortized cost of $15.1 million and a fair value of $16.6 million for Obligations of U.S. Government agencies issued by Ginnie Mae and an amortized cost of $683.6 million and a fair value of $676.9 million