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, 2017		78,006,956
Balance, beginning at Dec. 31, 2017	$ 1,199,057	$ 780	$ 797,997	$ 402,259	$ (1,979)
Net income	38,559			38,559
Other comprehensive income (loss)	(15,044)				(15,044)
Cash dividends declared	(19,476)			(19,476)
Stock issued in connection with acquisitions, shares		6,432,868
Stock issued in connection with acquisitions, value	250,807	$ 64	250,743
Stock issuances under stock incentive plans, shares		71,648
Stock issuances under stock incentive plans, value	0	$ 1	(1)
Stock-based compensation and related taxes	121		121
Balance, ending, shares at Mar. 31, 2018		84,511,472
Balance, ending at Mar. 31, 2018	$ 1,454,024	$ 845	1,048,860	421,342	(17,023)
Balance, beginning, shares at Dec. 31, 2018	84,521,692	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 (loss)	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	84,588,199
Balance, ending at Mar. 31, 2019	$ 1,550,850	$ 846	$ 1,051,299	474,818	$ 23,887
Cumulative-effect of accounting changes	$ (25,458)			$ (25,458)