Investment Securities - Held-to-maturity (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity securities transferred to available-for-sale securities			$ 52,400,000
Held-to-maturity securities transferred to available-for-sale securities, unrealized holding gains	$ 0	$ 0	$ 1,800,000	$ 0	$ 1,825,000
Held-to-maturity securities	$ 0			$ 0		$ 0