Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
BALANCE (in shares) at Dec. 31, 2018		25,494,328
BALANCE at Dec. 31, 2018	$ 1,095,700	$ 300	$ 292,800	$ 1,394,800	$ (137,800)	$ (454,400)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	38,600			38,600
Other comprehensive income (loss), net of taxes	(1,000)				(1,000)
Net issuance of treasury shares to employee stock compensation plans (in shares)		28,055
Net issuance of treasury shares to stock compensation plans	(800)		(11,700)			10,900
Stock-based compensation	6,100		6,100
Dividends declared	(4,800)			(4,800)
BALANCE (in shares) at Mar. 31, 2019		25,522,383
BALANCE at Mar. 31, 2019	1,127,700	$ 300	287,100	1,422,600	(138,700)	(443,500)
BALANCE (in shares) at Dec. 31, 2018		25,494,328
BALANCE at Dec. 31, 2018	1,095,700	$ 300	292,800	1,394,800	(137,800)	(454,400)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	38,600
BALANCE (in shares) at Dec. 31, 2019		25,486,711
BALANCE at Dec. 31, 2019	1,255,700	$ 300	295,300	1,542,400	(147,000)	(435,300)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	29,800
Other comprehensive income (loss), net of taxes	(59,000)				(59,000)
Purchases of treasury stock	(48,900)					(48,900)
Net issuance of treasury shares to employee stock compensation plans (in shares)		(38,436)
Net issuance of treasury shares to stock compensation plans	(2,500)		(12,700)			10,200
Stock-based compensation	5,100		5,100
Dividends declared	(5,500)			(5,500)
BALANCE (in shares) at Mar. 31, 2020		25,448,275
BALANCE at Mar. 31, 2020	$ 1,174,600	$ 300	$ 287,800	$ 1,566,700	$ (206,000)	$ (474,100)