Deposits - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Banking and Thrift [Abstract]
Deposits	$ 16,498,646		$ 15,505,383
Brokered deposits	8,600,000		8,200,000
Retail and other deposits	7,900,000		7,300,000
Stable interest-bearing deposits, total	5,800,000		5,500,000
Brokered deposit placement fee	2,800	$ 2,100
Third party broker fees paid	7,100	$ 2,100
Deposits exceeding FDIC insurance limits	404,500		395,500
Accrued interest on deposits	$ 36,800		$ 27,800