Deposits - Composition of Deposits and Interest Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	$ 4,876,611	$ 3,908,842	$ 3,672,308
Interest Expense	12,944	10,128	11,406
Noninterest-bearing Demand
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	1,227,766	1,083,919	992,779
Interest-bearing Demand
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	616,188	335,099	312,790
Interest Expense	818	19	75
Money Market
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	605,184	376,612	281,403
Interest Expense	1,299	572	446
Savings
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	1,061,265	1,027,095	994,805
Interest Expense	1,712	1,607	1,735
Certificates of Deposit
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	1,366,208	1,086,117	1,090,531
Interest Expense	$ 9,115	$ 7,930	$ 9,150