Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Minnesota-based Klein [Member]	Common Stock [Member]	Common Stock [Member] Minnesota-based Klein [Member]	Capital Surplus [Member]	Capital Surplus [Member] Minnesota-based Klein [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2016	$ 1,814,417		$ 135,159		$ 1,348,338		$ 390,292	$ (59,372)
Net income	95,725						95,725
Other comprehensive income (loss)	9,100							9,100
Acquisition	300,828		16,527		284,301
Dividends - common stock	(72,604)						(72,604)
Common stock issued	404		24		380
Common stock repurchased	(2,761)		(153)		(2,608)
Share-based compensation expense	6,275				6,275
Stock activity under incentive compensation plans	3,013		483		2,813		(283)
Ending Balance at Dec. 31, 2017	2,154,397		152,040		1,639,499		413,130	(50,272)
Cumulative effect of change in accounting principles	(4,179)						(4,127)	(52)
Balance, January 1	2,150,218		152,040		1,639,499		409,003	(50,324)
Reclassification of certain tax effects related to the Tax Cuts and Jobs Act of 2017							10,751	(10,751)
Net income	190,830						190,830
Other comprehensive income (loss)	16,125							16,125
Acquisition		$ 406,474		$ 22,772		$ 383,702
Dividends - common stock	(82,161)						(82,161)
Common stock issued	497		29		468
Common stock repurchased	(1,805)		(104)		(1,701)
Share-based compensation expense	8,118				8,118
Stock activity under incentive compensation plans	1,274		404		1,609		(739)
Ending Balance at Dec. 31, 2018	2,689,570		175,141		2,031,695		527,684	(44,950)
Cumulative effect of change in accounting principles	6,322						6,322	(52)
Balance, January 1	2,695,892		175,141		2,031,695		534,006	(44,950)
Net income	238,206						238,206
Other comprehensive income (loss)	101,157							101,157
Dividends - common stock	(89,474)						(89,474)
Common stock issued	567		36		531
Common stock repurchased	(102,413)		(6,174)		(96,239)
Share-based compensation expense	7,993				7,993
Stock activity under incentive compensation plans	525		613		465		(553)
Ending Balance at Dec. 31, 2019	$ 2,852,453		$ 169,616		$ 1,944,445		$ 682,185	$ 56,207