Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017		49,321,231
Beginning balance at Dec. 31, 2017	$ 1,514,983	$ 249,951	$ (19,906)	$ 898,095	$ 397,354	$ (10,511)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	33,826				33,826
Other comprehensive income (loss)	(6,985)					(6,985)
Comprehensive income	26,841
Cash dividends	(9,455)				(9,455)
Issuance of common stock for stock-based compensation awards (in shares)		71,747
Issuance of common stock for stock-based compensation awards	(1,482)		1,610	(3,092)
Stock-based compensation expense	1,858			1,858
Other, net	20			20
Ending balance (in shares) at Mar. 31, 2018		49,392,978
Ending balance at Mar. 31, 2018	1,532,765	$ 249,951	(18,296)	896,881	421,725	(17,496)
Beginning balance (in shares) at Dec. 31, 2017		49,321,231
Beginning balance at Dec. 31, 2017	1,514,983	$ 249,951	(19,906)	898,095	397,354	(10,511)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	70,536
Other comprehensive income (loss)	(9,541)
Comprehensive income	60,995
Ending balance (in shares) at Jun. 30, 2018		49,424,339
Ending balance at Jun. 30, 2018	1,558,668	$ 249,951	(17,523)	897,817	448,475	(20,052)
Beginning balance (in shares) at Mar. 31, 2018		49,392,978
Beginning balance at Mar. 31, 2018	1,532,765	$ 249,951	(18,296)	896,881	421,725	(17,496)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36,710				36,710
Other comprehensive income (loss)	(2,556)					(2,556)
Comprehensive income	34,154
Cash dividends	(9,960)				(9,960)
Issuance of common stock for stock-based compensation awards (in shares)		31,361
Issuance of common stock for stock-based compensation awards	(166)		773	(939)
Stock-based compensation expense	1,854			1,854
Other, net	21			21
Ending balance (in shares) at Jun. 30, 2018		49,424,339
Ending balance at Jun. 30, 2018	1,558,668	$ 249,951	(17,523)	897,817	448,475	(20,052)
Beginning balance (in shares) at Dec. 31, 2018		58,546,480
Beginning balance at Dec. 31, 2018	2,043,913	$ 296,483	(24,245)	1,288,911	500,660	(17,896)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	45,110				45,110
Other comprehensive income (loss)	10,446					10,446
Comprehensive income	55,556
Cash dividends	(12,442)				(12,442)
Issuance of common stock for stock-based compensation awards (in shares)		87,150
Issuance of common stock for stock-based compensation awards	(787)		2,655	(3,442)
Stock-based compensation expense	2,637			2,637
Ending balance (in shares) at Mar. 31, 2019		58,633,630
Ending balance at Mar. 31, 2019	2,088,877	$ 296,483	(21,590)	1,288,106	533,328	(7,450)
Beginning balance (in shares) at Dec. 31, 2018		58,546,480
Beginning balance at Dec. 31, 2018	2,043,913	$ 296,483	(24,245)	1,288,911	500,660	(17,896)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	91,735
Other comprehensive income (loss)	18,406
Comprehensive income	110,141
Ending balance (in shares) at Jun. 30, 2019		58,297,670
Ending balance at Jun. 30, 2019	2,119,696	$ 296,483	(33,635)	1,289,356	566,982	510
Beginning balance (in shares) at Mar. 31, 2019		58,633,630
Beginning balance at Mar. 31, 2019	2,088,877	$ 296,483	(21,590)	1,288,106	533,328	(7,450)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46,625				46,625
Other comprehensive income (loss)	7,960					7,960
Comprehensive income	54,585
Cash dividends	(12,971)				(12,971)
Repurchase of shares in connection with stock repurchase program (in shares)		(363,704)
Repurchase of shares in connection with stock repurchase program	(12,938)		(12,938)
Issuance of common stock for stock-based compensation awards (in shares)		27,744
Issuance of common stock for stock-based compensation awards	61		893	(832)
Stock-based compensation expense	2,082			2,082
Ending balance (in shares) at Jun. 30, 2019		58,297,670
Ending balance at Jun. 30, 2019	$ 2,119,696	$ 296,483	$ (33,635)	$ 1,289,356	$ 566,982	$ 510