Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]
Balance at period start (shares) at Dec. 31, 2016		31,299
Balance at period start at Dec. 31, 2016	$ 580,576	$ 313	$ 329,276	$ 406,932	$ (58,526)	$ (97,419)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee plans	(217)		(3,953)			3,736
Stock-based compensation	8,472		8,472
Dividends on common stock ($.80 per share)	(22,334)			(22,334)
Comprehensive income (loss):
Foreign currency translation adjustments					13,879
Pension liability (net of income tax expense/benefit)					645
Cash flow hedging gain (loss) (net of income tax expense/benefit)					(5,076)
Net income	55,487			55,487
Comprehensive income	64,935
Balance at period end (shares) at Dec. 31, 2017		31,299
Balance at period end at Dec. 31, 2017	631,432	$ 313	333,795	440,085	(49,078)	(93,683)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee plans	2,694		(2,094)			4,788
Stock-based compensation	10,037		10,037
Dividends on common stock ($.80 per share)	(22,477)			(22,477)
Comprehensive income (loss):
Foreign currency translation adjustments					(8,369)
Pension liability (net of income tax expense/benefit)					(672)
Cash flow hedging gain (loss) (net of income tax expense/benefit)					8,331
Net income	40,854			40,854
Comprehensive income	40,144
Balance at period end (shares) at Dec. 31, 2018		31,299
Balance at period end at Dec. 31, 2018	662,270	$ 313	341,738	464,851	(55,737)	(88,895)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee plans	4,315		(3,843)			8,158
Stock-based compensation	11,779		11,779
Dividends on common stock ($.80 per share)	(22,627)			(22,627)
Convertible notes discount, net	39,145		39,145
Convertible notes debt issuance costs	(1,233)		(1,233)
Convertible notes hedge, net	(38,829)		(38,829)
Issuance of warrants	30,567		30,567
Comprehensive income (loss):
Foreign currency translation adjustments					25
Pension liability (net of income tax expense/benefit)					27
Cash flow hedging gain (loss) (net of income tax expense/benefit)					(3,592)
Net income	28,620			28,620
Comprehensive income	25,080
Balance at period end (shares) at Dec. 31, 2019		31,299
Balance at period end at Dec. 31, 2019	$ 710,467	$ 313	$ 379,324	$ 470,844	$ (59,277)	$ (80,737)