Deposits - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deposits [Abstract]
Deposits	$ 15,505,383	$ 13,435,667
Brokered deposits	8,200,000	7,100,000
Retail and other deposits	7,300,000	6,300,000
Aggregate of deposits of individual depositors	5,500,000	5,400,000
Brokered deposit placement fee	9,400	10,100	$ 10,500
Third party broker fees paid	12,200	4,400	$ 4,100
Deposits exceeding FDIC insurance limits	395,500	304,500
Accrued interest on deposits	$ 27,800	$ 18,900