Deposits - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Banking and Thrift [Abstract]
Deposits	$ 16,745,957		$ 16,745,957		$ 15,505,383
Brokered deposits	8,700,000		8,700,000		8,200,000
Retail and other deposits	8,000,000		8,000,000		7,300,000
Stable interest-bearing deposits, total	5,700,000		5,700,000		5,500,000
Brokered deposit placement fee	3,000	$ 2,000	6,000	$ 4,000
Third party broker fees paid	12,000	$ 3,000	19,000	$ 5,000
Deposits exceeding FDIC insurance limits	406,000		406,000		396,000
Accrued interest on deposits	$ 39,000		$ 39,000		$ 28,000