Condensed Financial Information (parent company only) - Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flow From Operating Activities:
Net income	$ 47,830	$ 36,757	$ 41,056	$ 38,817	$ 41,713	$ 41,113	$ 39,634	$ 36,679	$ 164,460	$ 159,139	$ 96,070
Adjustments to Reconcile Net Income to Net Cash:
Share-based compensation									4,115	3,592	2,827
Net Change in:
Net cash provided by operating activities									178,407	180,235	126,502
Cash Flow From Investing Activities:
Net cash received in acquisition									10,207	0	54,536
Other									(8,564)	804	(4,047)
Net cash used in investing activities									(1,006,399)	(575,576)	(635,330)
Cash Flows from Financing Activities:
Stock issued under employee benefit plans									702	707	519
Stock issued under dividend reinvestment and stock purchase plan									1,531	1,211	991
Stock options exercised									144	1,598	2,398
Restricted shares withheld for taxes									(1,680)	(1,902)	(1,283)
Repurchase of common stock									(19,041)	0	0
Net cash provided by financing activities									865,946	379,683	535,806
Net Change in Cash and Cash Equivalents									37,954	(15,658)	26,978
Cash and Cash Equivalents, January 1				139,247				154,905	139,247	154,905	127,927
Cash and Cash Equivalents, December 31	177,201				139,247				177,201	139,247	154,905
Parent
Cash Flow From Operating Activities:
Net income									164,460	159,139	96,070
Adjustments to Reconcile Net Income to Net Cash:
Share-based compensation									1,339	1,256	1,215
Distributions in excess of (equity in undistributed) income of subsidiaries									(51,368)	(68,329)	(71,164)
Loss on sale of available for sale securities									0	0	50
Net Change in:
Other assets									(8,944)	584	3,358
Other liabilities									4,611	274	(1,900)
Investment in subsidiaries - operating activities									(268)	841	1,112
Net cash provided by operating activities									109,830	93,765	28,741
Cash Flow From Investing Activities:
Net cash received in acquisition									78	0	37
Other									0	2,189	0
Net cash used in investing activities									78	2,189	37
Cash Flows from Financing Activities:
Cash dividends									(51,276)	(41,660)	(31,820)
Stock issued under employee benefit plans									702	707	519
Stock issued under dividend reinvestment and stock purchase plan									1,531	1,211	991
Stock options exercised									144	1,598	2,398
Restricted shares withheld for taxes									(1,680)	(1,902)	(1,283)
Repurchase of common stock									(19,041)	0	0
Net cash provided by financing activities									(69,620)	(40,046)	(29,195)
Net Change in Cash and Cash Equivalents									40,288	55,908	(417)
Cash and Cash Equivalents, January 1				$ 87,435				$ 31,527	87,435	31,527	31,944
Cash and Cash Equivalents, December 31	$ 127,723				$ 87,435				$ 127,723	$ 87,435	$ 31,527