Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock Outstanding [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance (in shares) at Dec. 31, 2016	79,610,277
Balance at Dec. 31, 2016	$ 878	$ 895,480	$ (3,715)	$ 1,175,485	$ (239,589)	$ 1,828,539
Dividend Reinvestment Plan (in shares)	65,044					65,044
Dividend Reinvestment Plan	$ 1	2,527	0	0	0	$ 2,528
Restricted stock units vested (in shares)	224,995
Restricted stock units vested	$ 2	0	0	0	0	2
Warrants exercised (in shares)	4,681
Warrants exercised	$ 0	0	0	0	0	0
Shares withheld related to net share settlement of RSUs	$ 0	(6,813)	0	0	0	(6,813)
Stock issued to directors (in shares)	15,400
Stock issued to directors	$ 0	550	0	0	0	$ 550
Stock options exercised (in shares)	46,790					46,790
Stock options exercised	$ 1	1,093	0	0	0	$ 1,094
Equity consideration for acquisition (in shares)	926,192
Equity consideration for acquisition	$ 9	34,853	0	0	0	34,862
Stock -based compensation	0	5,184	0	0	0	5,184
Cash dividends	0	0	0	(69,888)	0	(69,888)
Change in other comprehensive loss	0	0	1,204	0	0	1,204
Net income	$ 0	0	0	176,042	0	176,042
Balance (in shares) at Dec. 31, 2017	80,893,379
Balance at Dec. 31, 2017	$ 891	932,874	(2,511)	1,281,639	(239,589)	$ 1,973,304
Dividend Reinvestment Plan (in shares)	69,084					69,084
Dividend Reinvestment Plan	$ 1	2,821	0	0	0	$ 2,822
Restricted stock units vested (in shares)	125,207
Restricted stock units vested	$ 1	0	0	0	0	1
Warrants exercised (in shares)	476,064
Warrants exercised	$ 5	(5)	0	0	0	0
Shares withheld related to net share settlement of RSUs	$ 0	(2,440)	0	0	0	(2,440)
Stock issued to directors (in shares)	16,060
Stock issued to directors	$ 0	649	0	0	0	$ 649
Stock options exercised (in shares)	35,880					35,880
Stock options exercised	$ 0	838	0	0	0	$ 838
Stock -based compensation	0	7,325	0	0	0	7,325
Cash dividends	0	0	0	(83,446)	0	(83,446)
Change in other comprehensive loss	0	0	(6,424)	0	0	(6,424)
Net income	0	0	0	271,885	0	271,885
Cumulative effect of changes in accounting principles	0	0	(8,556)	8,556	0	0
Reclassification of tax effects in accumulated other comprehensive income resulting from the new corporate income tax rate	$ 0	0	(515)	515	0	0
Purchases of treasury stock (in shares)	(1,113,726)
Purchases of treasury stock	$ 0	0	0	0	(42,648)	(42,648)
Balance (in shares) at Dec. 31, 2018	80,501,948
Balance at Dec. 31, 2018	$ 898	942,062	(18,006)	1,479,149	(282,237)	$ 2,121,866
Dividend Reinvestment Plan (in shares)	93,143					93,143
Dividend Reinvestment Plan	$ 1	3,365	0	0	0	$ 3,366
Restricted stock units vested (in shares)	123,762
Restricted stock units vested	$ 1	0	0	0	0	1
Shares withheld related to net share settlement of RSUs	$ 0	(2,311)	0	0	0	(2,311)
Stock issued to directors (in shares)	21,160
Stock issued to directors	$ 0	749	0	0	0	749
Stock -based compensation	0	6,601	0	0	0	6,601
Cash dividends	0	0	0	(99,131)	0	(99,131)
Change in other comprehensive loss	0	0	20,308	0	0	20,308
Net income	$ 0	0	0	279,135	0	279,135
Purchases of treasury stock (in shares)	(1,010,594)
Purchases of treasury stock	$ 0	0	0	0	(36,301)	(36,301)
Balance (in shares) at Dec. 31, 2019	79,729,419
Balance at Dec. 31, 2019	$ 900	$ 950,466	$ 2,302	$ 1,659,153	$ (318,538)	$ 2,294,283