Deposits - Narrative (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Time Deposits [Line Items]
Demand, non-interest bearing	$ 1,052,115	$ 966,058
Savings, including money market deposit accounts	3,318,486	3,166,557
Time deposits greater than $250,000	800,000	1,200,000
Brokered money market deposits	654,800	972,200
Brokered certificates of deposit	504,300	721,900
Demand deposit overdrafts reclassified as loans	$ 2,000	12,300
Held and Used
Time Deposits [Line Items]
Demand, non-interest bearing		453,400
Savings, including money market deposit accounts		$ 3,400