Unaudited Condensed 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 Compre- hensive Income
Balance, beginning (in shares) at Dec. 31, 2019			92,289,750
Balance, beginning at Dec. 31, 2019	$ 1,960,733	$ (12,347)	$ 923	$ 1,378,534	$ 541,050	$ (12,347)	$ 40,226
Increase (Decrease) in Stockholders' Equity
Net income	43,339				43,339
Other comprehensive income (loss)	59,498						59,498
Cash dividends declared	(27,727)				(27,727)
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)			111,480
Stock issuances under stock incentive plans	0		$ 1	(1)
Stock-based compensation and related taxes	1,015			1,015
Balance, ending (in shares) at Mar. 31, 2020			95,408,274
Balance, ending at Mar. 31, 2020	$ 2,136,644		$ 954	1,491,651	544,315		99,724
Balance, beginning (in shares) at Dec. 31, 2020	95,426,364		95,426,364
Balance, beginning at Dec. 31, 2020	$ 2,307,041		$ 954	1,495,053	667,944		143,090
Increase (Decrease) in Stockholders' Equity
Net income	80,802				80,802
Other comprehensive income (loss)	(63,170)						(63,170)
Cash dividends declared	(29,674)				(29,674)
Stock issuances under stock incentive plans (in shares)			75,455
Stock issuances under stock incentive plans	0		$ 1	(1)
Stock-based compensation and related taxes	$ 386			386
Balance, ending (in shares) at Mar. 31, 2021	95,501,819		95,501,819
Balance, ending at Mar. 31, 2021	$ 2,295,385		$ 955	$ 1,495,438	$ 719,072		$ 79,920