Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Paid-in Capital	Retained Earnings Substantially Restricted	Retained Earnings Substantially Restricted Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive (Loss) Income
Balance (in shares) at Dec. 31, 2017			78,006,956
Balance at Dec. 31, 2017	$ 1,199,057		$ 780	$ 797,997	$ 402,259		$ (1,979)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	181,878				181,878
Other comprehensive (loss) income	(7,448)				0		(7,448)
Cash dividends declared	(110,954)				(110,954)
Stock issued in connection with acquisitions (in shares)			6,432,868
Stock issued in connection with acquisitions	250,807		$ 64	250,743
Stock issuances under stock incentive plans (in shares)			81,868
Stock issuances under stock incentive plans	0		$ 1	(1)
Stock-based compensation and related taxes	2,514			2,514
Balance (in shares) at Dec. 31, 2018			84,521,692
Balance at Dec. 31, 2018	1,515,854	$ (25,114)	$ 845	1,051,253	473,183	$ (25,114)	(9,427)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	210,544				210,544
Other comprehensive (loss) income	49,653						49,653
Cash dividends declared	(117,563)				(117,563)
Stock issued in connection with acquisitions (in shares)			7,519,617
Stock issued in connection with acquisitions	316,538		$ 75	316,463
Stock issuances under stock incentive plans (in shares)			248,441
Stock issuances under stock incentive plans	0		$ 3	(3)
Stock-based compensation and related taxes	$ 10,821			10,821
Balance (in shares) at Dec. 31, 2019	92,289,750		92,289,750
Balance at Dec. 31, 2019	$ 1,960,733	$ (12,347)	$ 923	1,378,534	541,050	$ (12,347)	40,226
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	266,400				266,400
Other comprehensive (loss) income	102,864						102,864
Cash dividends declared	(127,159)				(127,159)
Stock issued in connection with acquisitions (in shares)			3,007,044
Stock issued in connection with acquisitions	112,133		$ 30	112,103
Stock issuances under stock incentive plans (in shares)			129,570
Stock issuances under stock incentive plans	0		$ 1	(1)
Stock-based compensation and related taxes	$ 4,417			4,417
Balance (in shares) at Dec. 31, 2020	95,426,364		95,426,364
Balance at Dec. 31, 2020	$ 2,307,041		$ 954	$ 1,495,053	$ 667,944		$ 143,090