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	102,500
Other comprehensive income (loss)	(13,712)
Comprehensive income	88,788
Ending balance (in shares) at Sep. 30, 2018		58,743,814
Ending balance at Sep. 30, 2018	2,010,711	$ 296,484	(17,225)	1,287,063	468,612	(24,223)
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31,964				31,964
Other comprehensive income (loss)	(4,171)					(4,171)
Comprehensive income	27,793
Cash dividends	(11,827)				(11,827)
Common stock issued in connection with an acquisition (in shares)		9,304,477
Common stock issued in connection with an acquisition	434,519	$ 46,533		387,986
Issuance of common stock for stock-based compensation awards (in shares)		14,998
Issuance of common stock for stock-based compensation awards	(306)		298	(604)
Stock-based compensation expense	1,844			1,844
Other, net	20			20
Ending balance (in shares) at Sep. 30, 2018		58,743,814
Ending balance at Sep. 30, 2018	2,010,711	$ 296,484	(17,225)	1,287,063	468,612	(24,223)
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	129,181
Other comprehensive income (loss)	19,590
Comprehensive income	148,771
Ending balance (in shares) at Sep. 30, 2019		57,455,306
Ending balance at Sep. 30, 2019	2,119,659	$ 296,483	(62,044)	1,291,927	591,599	1,694
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 stock 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,446				37,446
Other comprehensive income (loss)	1,184					1,184
Comprehensive income	38,630
Cash dividends	(12,829)				(12,829)
Repurchase of stock in connection with stock repurchase program (in shares)		(851,421)
Repurchase of shares in connection with stock repurchase program	(28,707)		(28,707)
Issuance of common stock for stock-based compensation awards (in shares)		9,057
Issuance of common stock for stock-based compensation awards	(133)		298	(431)
Stock-based compensation expense	3,002			3,002
Ending balance (in shares) at Sep. 30, 2019		57,455,306
Ending balance at Sep. 30, 2019	$ 2,119,659	$ 296,483	$ (62,044)	$ 1,291,927	$ 591,599	$ 1,694