Income Taxes - Reconciliation of Effective Income Tax (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory tax rate (as a percent)									21.00%	35.00%	35.00%
Income tax expense at Federal statutory rate									$ 13,502	$ 21,051	$ 18,452
Tax-exempt instruments									(1,879)	(3,212)	(3,198)
Non-deductible acquisition costs									336	210	0
Federal tax credits and other benefits									(515)	(1,510)	(931)
Effects of BOLI									(330)	(531)	(511)
Revaluation of net deferred tax assets										2,568	0
Other, net									(84)	(220)	(9)
Income tax expense	$ 4,618	$ 3,010	$ 2,003	$ 1,399	$ 7,270	$ 3,922	$ 4,075	$ 3,089	11,030	18,356	13,803
Amortizaon of LIHTC									$ 3,100	$ 2,200	$ 523