Dividend Restrictions - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Restrictions On Dividends Loans And Advances Disclosure [Abstract]
Amount available for payment of dividend without prior approval	$ 105,453	$ 66,180
Dividends declared	$ 0	$ 69,300	$ 23,600