Unaudited Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings Substantially Restricted	Accumulated Other Comprehensive (Loss) Income
Balance, beginning, shares at Dec. 31, 2018		84,521,692
Balance, beginning at Dec. 31, 2018	$ 1,515,854	$ 845	$ 1,051,253	$ 473,183	$ (9,427)
Net income	49,132			49,132
Other comprehensive income	33,314				33,314
Cash dividends declared	(22,039)			(22,039)
Stock issuances under stock incentive plans, shares		66,507
Stock issuances under stock incentive plans, value	0	$ 1	(1)
Stock-based compensation and related taxes	47		47
Balance, ending, shares at Mar. 31, 2019		84,588,199
Balance, ending at Mar. 31, 2019	1,550,850	$ 846	1,051,299	474,818	23,887
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (25,458)			(25,458)
Balance, beginning, shares at Dec. 31, 2019	92,289,750	92,289,750
Balance, beginning at Dec. 31, 2019	$ 1,960,733	$ 923	1,378,534	541,050	40,226
Net income	43,339			43,339
Other comprehensive income	59,498				59,498
Cash dividends declared	(27,727)			(27,727)
Stock issuances under stock incentive plans, shares		111,480
Stock issuances under stock incentive plans, value	0	$ 1	(1)
Stock issued in connection with acquisitions, shares		3,007,044
Stock issued in connection with acquisitions, value	112,133	$ 30	112,103
Stock-based compensation and related taxes	$ 1,015		1,015
Balance, ending, shares at Mar. 31, 2020	95,408,274	95,408,274
Balance, ending at Mar. 31, 2020	$ 2,136,644	$ 954	$ 1,491,651	544,315	$ 99,724
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (12,347)			$ (12,347)