Deposits - Composition of Deposits and Interest Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	$ 5,673,922	$ 5,427,891	$ 5,272,377
Interest Expense	40,856	25,330	19,692
Noninterest-bearing demand
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	1,421,156	1,387,712	1,263,833
Interest Expense	0	0	0
Interest-bearing demand
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	573,693	603,141	638,300
Interest Expense	93	67	111
Money market
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	1,482,065	1,146,156	936,461
Interest Expense	20,018	9,204	4,199
Savings
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	784,970	893,119	1,050,131
Interest Expense	1,773	2,081	2,002
Certificates of deposit
Schedule Of Deposits And Borrowings Maturities [Line Items]
Balance	1,412,038	1,397,763	1,383,652
Interest Expense	$ 18,972	$ 13,978	$ 13,380