Securities - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities pledged as collateral		$ 1,300,000,000	$ 1,100,000,000
Held-to-maturity securities pledged as collateral		0	0
Carrying value of securities sold	$ 210,200,000
OTTI balance		$ 23,300,000	$ 23,300,000