Investment Securities - Gains and (Losses) Recognized in Earnings (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)
Investments, Debt and Equity Securities [Abstract]
Securities in unrealized loss positions, qualitative disclosure, number of positions (in security) | security	1,366		1,366
Proceeds	$ 7,035	$ 2,820	$ 17,085	$ 7,820
Gross gains	1	17	168	54
Gross losses	$ 0	$ (1)	$ 0	$ (1)