General – Cumulative Effect of Changes for Adoption of ASU 2014-09 (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Other current assets	$ 108,872	$ 71,656	$ 72,323
Total Current Assets	1,618,846	1,482,686	1,483,353
Deferred income taxes	1,128	2,148	813
Other long-term assets	21,489	21,234	22,567
Total Assets	3,091,737	2,956,569	2,957,234
LIABILITIES AND STOCKHOLDERS' EQUITY
Accrued liabilities	246,909	191,453	193,635
Total Current Liabilities	985,701	890,121	892,303
Deferred credits and other long-term liabilities	36,148	24,844	19,100
Total Liabilities	1,786,608	1,684,302	1,680,740
Retained earnings	1,406,720	1,395,268	1,399,495
Total Stockholders' Equity	1,305,129	1,272,267	1,276,494
Total Liabilities and Stockholders' Equity	3,091,737	2,956,569	$ 2,957,234
Adjustments | ASU 2014-09
Assets
Other current assets	(297)	(667)
Total Current Assets	(28,633)	(667)
Deferred income taxes		1,335
Other long-term assets	9,483	(1,333)
Total Assets	(19,150)	(665)
LIABILITIES AND STOCKHOLDERS' EQUITY
Accrued liabilities	(21,154)	(2,182)
Total Current Liabilities	(21,154)	(2,182)
Deferred credits and other long-term liabilities	(6,289)	5,744
Total Liabilities	(27,443)	3,562
Retained earnings	8,293	(4,227)
Total Stockholders' Equity	8,293	(4,227)
Total Liabilities and Stockholders' Equity	$ (19,150)	$ (665)