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
Payment of cash dividends	(30,589)
Ending Balance at Dec. 31, 2018	$ 3,505,423	$ 2,673	2,827,154	1,753,557	2,487	(1,080,448)
Ending 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
Exercise of stock options (in shares)	0
Vesting of restricted stock units (in shares)		38,000
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	267,353,108	267,353,000