Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2016	51,485,090
Balance at Dec. 31, 2016	$ 515	$ 983,532	$ 313,952	$ 22,071	$ 1,320,070
Net Income	0	0	141,835	0	141,835
Other comprehensive loss, net of tax	$ 0	0	0	(18,079)	(18,079)
Total comprehensive income					123,756
Shares issued under stock-based compensation programs, net (in shares)	492,408
Shares issued under stock-based compensation programs, net	$ 5	9,496	0	0	9,501
Cash dividends declared	$ 0	0	(51,779)	0	(51,779)
Stock dividend declared (in shares)	4,151,722
Stock dividend declared	$ 41	145,685	(145,844)	0	(118)
Stock-based compensation expense	$ 0	5,857	0	0	5,857
Forfeiture of restricted stock (in shares)	(5,992)
Forfeiture of restricted stock	$ 0	0	0	0	0
Balance (in shares) at Dec. 31, 2017	56,123,228
Balance at Dec. 31, 2017	$ 561	1,144,570	258,164	3,992	1,407,287
Net Income	$ 0	0	210,780	0	210,780
Shares issued under stock-based compensation programs, net (in shares)	497,024
Shares issued under stock-based compensation programs, net	$ 5	9,855	0	0	9,860
Cash dividends declared	0	0	(67,718)	0	(67,718)
Stock-based compensation expense	$ 0	14,017	0	0	14,017
Forfeiture of restricted stock (in shares)	(4,900)
Forfeiture of restricted stock	$ 0	0	0	0	0
Cumulative effect of newly adopted accounting standards at Dec. 31, 2017	0	0	5,766	(3,992)	1,774
Adjusted Balance at Dec. 31, 2017	$ 561	1,144,570	263,930	0	1,409,061
Balance (in shares) at Dec. 31, 2018	56,615,352
Balance at Dec. 31, 2018	$ 566	1,168,442	406,992	0	1,576,000
Net Income	$ 0	0	238,312	0	238,312
Shares issued under stock-based compensation programs, net (in shares)	1,429,993
Shares issued under stock-based compensation programs, net	$ 15	15,326	0	0	15,341
Cash dividends declared	$ 0	0	(73,020)	0	(73,020)
Stock dividend declared (in shares)	4,534,908
Stock dividend declared	$ 45	138,949	(139,091)	0	(97)
Stock-based compensation expense	$ 0	26,016	0	0	26,016
Forfeiture of restricted stock (in shares)	(5,292)
Forfeiture of restricted stock	$ 0	0	0	0	0
Cumulative effect of newly adopted accounting standards at Dec. 31, 2018	0	0	(67)	0	(67)
Adjusted Balance at Dec. 31, 2018	$ 566	1,168,442	406,925	0	1,575,933
Balance (in shares) at Dec. 31, 2019	62,574,961
Balance at Dec. 31, 2019	$ 626	$ 1,348,733	$ 433,126	$ 0	$ 1,782,485