Parent Company Financial Statements, Condensed Statements of Income and Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Expenses [Abstract]
Interest expense	$ 25,450	$ 40,513	$ 29,295
Other expenses	12,031	12,539	15,558
Income before income taxes and equity in undistributed income of subsidiaries	70,265	71,992	70,542
Income tax benefit	10,761	7,452	11,314
Net income	59,504	64,540	59,228
Unrealized holding gains (losses) on securities available-for-sale [Abstract]
Unrealized holding gains (losses) arising during the period	13,839	14,270	(5,393)
Less: Reclassification adjustments for realized gains (losses) included in net income	1,251	3	(821)
Other comprehensive income (loss), net of tax	9,315	10,864	(3,612)
Comprehensive income	68,819	75,404	55,616
Parent Company [Member]
Income [Abstract]
Dividends from subsidiaries	29,593	30,152	26,750
Other income	476	757	489
Total income	30,069	30,909	27,239
Expenses [Abstract]
Interest expense	1,519	2,520	2,318
Depreciation expense	112	144	135
Other expenses	3,302	3,273	3,156
Total expenses	4,933	5,937	5,609
Income before income taxes and equity in undistributed income of subsidiaries	25,136	24,972	21,630
Income tax benefit	(576)	(4,947)	(1,219)
Income before equity in undistributed income of subsidiaries	25,712	29,919	22,849
Equity in undistributed income of subsidiaries	33,792	34,621	36,379
Net income	59,504	64,540	59,228
Unrealized holding gains (losses) on securities available-for-sale [Abstract]
Unrealized holding gains (losses) arising during the period	13,839	14,270	(5,393)
Less: Reclassification adjustments for realized gains (losses) included in net income	1,251	3	(821)
Tax expense (benefit)	3,273	3,403	(960)
Other comprehensive income (loss), net of tax	9,315	10,864	(3,612)
Comprehensive income	$ 68,819	$ 75,404	$ 55,616