Income Taxes - Reconciliation of Expected Tax Benefit with Income Tax Benefit Relating to Loss before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax rate applied to income before income taxes	$ 27,720	$ 15,431	$ 12,484
Increase (decrease) resulting from the effects of:
Tax law change	8,552	0	0
Nondeductible acquisition costs	657	217	441
Tax exempt interest on obligations of states and political subdivisions and bank owned life insurance	(1,445)	(1,215)	(761)
State income taxes	(1,007)	(726)	(746)
Nontaxable bargain purchase gain	0	0	(146)
Tax credit investments	(165)	(55)	0
Stock compensation	(1,027)	(731)	127
Other	173	(105)	(3)
Federal tax provision	33,458	12,816	11,396
State tax provision	2,878	2,073	2,131
Total income tax provision	$ 36,336	$ 14,889	$ 13,527