CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning Balance at Dec. 31, 2017	$ 3,982,493	$ 2,662	$ 2,785,823	$ 2,105,897	$ 6,822	$ (918,711)
Beginning Balance (in shares) at Dec. 31, 2017		266,259,000
Net loss	(34,417)			(34,417)
Foreign currency translation adjustment	(1,984)				(1,984)
Exercise of stock options	485	$ 1	484
Exercise of stock options (in shares)		40,000
Stock-based compensation	9,365		9,365
Payment of cash dividends	(4,443)			(4,443)
Dividend equivalents	(30)			(30)
Purchase of treasury stock	(16,928)					(16,928)
Ending Balance at Mar. 31, 2018	3,934,541	$ 2,663	2,795,672	2,067,007	4,838	(935,639)
Ending Balance (in shares) at Mar. 31, 2018		266,299,000
Beginning Balance at Dec. 31, 2017	3,982,493	$ 2,662	2,785,823	2,105,897	6,822	(918,711)
Beginning Balance (in shares) at Dec. 31, 2017		266,259,000
Net loss	(45,130)			(45,130)
Foreign currency translation adjustment	(3,514)				(3,514)
Exercise of stock options	485	$ 1	484
Exercise of stock options (in shares)		40,000
Issuance of common stock		$ 4	(4)
Issuance of common stock (in shares)		381,000
Vesting of restricted stock units (in shares)		10,000
Forfeitures of restricted stock (in shares)		(2,000)
Stock-based compensation	19,272		19,272
Payment of cash dividends	(13,275)			(13,275)
Dividend equivalents	(113)			(113)
Purchase of treasury stock	(59,879)					(59,879)
Ending Balance at Jun. 30, 2018	3,880,339	$ 2,667	2,805,575	2,047,379	3,308	(978,590)
Ending Balance (in shares) at Jun. 30, 2018		266,688,000
Beginning Balance at Mar. 31, 2018	3,934,541	$ 2,663	2,795,672	2,067,007	4,838	(935,639)
Beginning Balance (in shares) at Mar. 31, 2018		266,299,000
Net loss	(10,713)			(10,713)
Foreign currency translation adjustment	(1,530)				(1,530)
Issuance of common stock		$ 4	(4)
Issuance of common stock (in shares)		381,000
Forfeitures of restricted stock (in shares)		(2,000)
Stock-based compensation	9,907		9,907
Payment of cash dividends	(8,832)			(8,832)
Dividend equivalents	(83)			(83)
Purchase of treasury stock	(42,951)					(42,951)
Ending Balance at Jun. 30, 2018	3,880,339	$ 2,667	2,805,575	2,047,379	3,308	(978,590)
Ending Balance (in shares) at Jun. 30, 2018		266,688,000
Beginning Balance at Dec. 31, 2018	$ 3,505,423	$ 2,673	2,827,154	1,753,557	2,487	(1,080,448)
Beginning Balance (in shares) at Dec. 31, 2018	267,315,526	267,316,000
Net loss	$ (28,614)			(28,614)
Foreign currency translation adjustment	944				944
Forfeitures of restricted stock (in shares)		(1,000)
Stock-based compensation	9,338		9,338
Payment of cash dividends	(8,499)			(8,499)
Dividend equivalents	(110)			(110)
Purchase of treasury stock	(75,113)					(75,113)
Ending Balance at Mar. 31, 2019	3,403,369	$ 2,673	2,836,492	1,716,334	3,431	(1,155,561)
Ending Balance (in shares) at Mar. 31, 2019		267,353,000
Beginning Balance at Dec. 31, 2018	$ 3,505,423	$ 2,673	2,827,154	1,753,557	2,487	(1,080,448)
Beginning Balance (in shares) at Dec. 31, 2018	267,315,526	267,316,000
Net loss	$ (78,061)			(78,061)
Foreign currency translation adjustment	1,792				1,792
Exercise of stock options	$ 9,219	$ 7	9,212
Exercise of stock options (in shares)	700,000	700,000
Vesting of restricted stock units		$ 8	(8)
Vesting of restricted stock units (in shares)		777,000
Forfeitures of restricted stock (in shares)		(2,000)
Stock-based compensation	$ 20,388		20,388
Payment of cash dividends	(16,843)			(16,843)
Dividend equivalents	(236)			(236)
Purchase of treasury stock	(163,371)					(163,371)
Ending Balance at Jun. 30, 2019	$ 3,278,311	$ 2,688	2,856,746	1,658,417	4,279	(1,243,819)
Ending Balance (in shares) at Jun. 30, 2019	268,790,705	268,791,000
Beginning Balance at Mar. 31, 2019	$ 3,403,369	$ 2,673	2,836,492	1,716,334	3,431	(1,155,561)
Beginning Balance (in shares) at Mar. 31, 2019		267,353,000
Net loss	(49,447)			(49,447)
Foreign currency translation adjustment	848				848
Exercise of stock options	9,219	$ 7	9,212
Exercise of stock options (in shares)		700,000
Forfeitures of restricted stock (in shares)		(1,000)
Stock-based compensation	11,050		11,050
Payment of cash dividends	(8,344)			(8,344)
Dividend equivalents	(126)			(126)
Purchase of treasury stock	(88,258)					(88,258)
Ending Balance at Jun. 30, 2019	$ 3,278,311	$ 2,688	$ 2,856,746	$ 1,658,417	$ 4,279	$ (1,243,819)
Ending Balance (in shares) at Jun. 30, 2019	268,790,705	268,791,000