Parent Company Financial Statements, Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities [Abstract]
Net income	$ 59,504	$ 64,540	$ 59,228
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Depreciation	5,346	5,515	3,786
Deferred taxes	(2,909)	(1,412)	(246)
Stock-based compensation	944	859	710
Gain on debt repurchase	0	(219)	0
Changes in [Abstract]
Other assets	1,845	4,941	(14,694)
Other liabilities	4,147	(2,440)	9,660
Net cash provided by operating activities	62,379	83,458	65,487
Cash flows from investing activities [Abstract]
Purchase of premises and equipment	(1,482)	(2,570)	(2,832)
Net cash used in investing activities	(693,526)	(34,491)	(100,590)
Cash flows from financing activities [Abstract]
Issuance of common stock	926	1,264	1,230
Repurchase of common stock	(1,099)	0	0
Dividends paid	(27,142)	(26,235)	(24,395)
Net cash provided by (used in) financing activities	704,699	74,266	1,279
Cash and cash equivalents at beginning of year	264,683
Cash and cash equivalents at end of year	338,235	264,683
Parent Company [Member]
Cash flows from operating activities [Abstract]
Net income	59,504	64,540	59,228
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Depreciation	112	144	135
Equity in undistributed earnings of subsidiaries	(33,792)	(34,621)	(36,379)
Deferred taxes	451	(4,907)	(12)
Stock-based compensation	944	859	710
Gain on debt repurchase	0	(219)	0
Changes in [Abstract]
Other assets	(115)	1	(50)
Other liabilities	(318)	683	53
Net cash provided by operating activities	26,786	26,480	23,685
Cash flows from investing activities [Abstract]
Payment for investment in subsidiary	0	(1,281)	0
Purchase of premises and equipment	(55)	(78)	(81)
Net cash used in investing activities	(55)	(1,359)	(81)
Cash flows from financing activities [Abstract]
Issuance of common stock	926	1,264	1,230
Repurchase of common stock	(1,099)	0	0
Dividends paid	(27,142)	(26,235)	(24,395)
Net cash provided by (used in) financing activities	(27,315)	(24,971)	(23,165)
Net increase (decrease) in cash and cash equivalents	(584)	150	439
Cash and cash equivalents at beginning of year	2,089	1,939	1,500
Cash and cash equivalents at end of year	$ 1,505	$ 2,089	$ 1,939