Investment Securities - Textual (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Securities valued at less than historical cost, amount	$ 710,600,000		$ 710,600,000		$ 1,700,000,000
Securities valued at less than historical cost (as percent)	29.60%		29.60%		70.30%
Securities pledged as collateral	$ 1,120,000,000		$ 1,120,000,000		$ 1,020,000,000.00
Realized gains	7,600,000	$ 41,000	12,900,000	$ 54,000
Realized losses	3,000	$ 0	$ 3,000	$ 1,000
Bonds
Debt Securities, Available-for-sale [Line Items]
Realized gains	7,300,000
Bonds sold, amount	$ 89,000,000