Investment Securities - Textual (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Securities valued at less than historical cost, amount	$ 1,000,000,000.0		$ 1,000,000,000.0		$ 1,700,000,000
Securities valued at less than historical cost (as percent)	39.80%		39.80%		70.30%
Securities pledged as collateral	$ 1,180,000,000		$ 1,180,000,000		$ 1,020,000,000.00
Realized gains	2,800,000	$ 7,000	5,600,000	$ 13,000
Realized losses	$ 0	$ 14,000	$ 0	$ 14,000