Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income
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, 2019		56,855,002
Beginning balance at Dec. 31, 2019	2,125,689	$ 296,483	(83,189)	1,294,276	617,355	764
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,008				2,008
Other comprehensive income (loss)	13,737					13,737
Comprehensive income	15,745
Cash dividends	(12,555)				(12,555)
Repurchase of shares in connection with stock repurchase program (in shares)		(818,886)
Repurchase of shares in connection with stock repurchase program	(24,569)		(24,569)
Issuance of common stock for stock-based compensation awards (in shares)		104,902
Issuance of common stock for stock-based compensation awards	(1,449)		4,138	(5,587)
Stock-based compensation expense	2,750			2,750
Ending balance (in shares) at Mar. 31, 2020		56,141,018
Ending balance at Mar. 31, 2020	$ 2,070,512	$ 296,483	$ (103,620)	$ 1,291,439	$ 571,709	$ 14,501