Parent Company Condensed Financial Information - Statements of Net Income (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
Condensed Income Statements, Captions [Line Items]
Total Interest Income	$ 76,589	$ 73,627	$ 71,581	$ 68,029	$ 67,855	$ 66,723	$ 64,914	$ 61,150	$ 289,826	$ 260,642	$ 227,774
Interest expense on long-term debt									1,129	463	670
Income tax benefit	$ 4,952	$ 2,876	$ 4,010	$ 6,007	$ 22,255	$ 8,883	$ 8,604	$ 6,695	17,845	46,437	25,305
Net Income									105,334	72,968	71,392
Parent Company
Condensed Income Statements, Captions [Line Items]
Dividends from subsidiaries									44,988	36,169	34,134
Investment income									24	22	17
Total Interest Income									45,012	36,191	34,151
Interest expense on long-term debt									1,149	955	854
Other expenses									3,988	3,801	4,012
Total Expense									5,137	4,756	4,866
Income before income tax and undistributed net income of subsidiaries									39,875	31,435	29,285
Income tax benefit									(1,093)	(1,596)	(1,697)
Income before undistributed net income of subsidiaries									40,968	33,031	30,982
Equity in undistributed net income (distribution in excess of net income) of bank subsidiary									68,385	40,877	40,051
Equity in undistributed net income (distribution in excess of net income) of nonbank subsidiaries									(4,019)	(940)	359
Net Income									$ 105,334	$ 72,968	$ 71,392