General – Impact of Adoption of ASC 842 on Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets
Other long-term assets	$ 90,997	$ 84,350	$ 24,530
Total Assets	3,071,157	3,038,928	2,979,056
LIABILITIES AND STOCKHOLDERS' EQUITY
Accrued liabilities	260,954	244,374	231,356
Total Current Liabilities	943,858	911,911	898,893
Deferred credits and other long-term liabilities	81,022	83,482	36,483
Total Liabilities	1,777,767	1,753,770	1,693,753
Retained earnings	1,419,735	1,419,304	1,419,449
Total Stockholders' Equity	1,293,390	1,285,158	1,285,303
Total Liabilities and Stockholders' Equity	3,071,157	3,038,928	$ 2,979,056
ASU 2016-02 | Adjustments
Assets
Other long-term assets	(56,008)	59,820
Total Assets	(56,008)	59,872
LIABILITIES AND STOCKHOLDERS' EQUITY
Accrued liabilities	(12,555)	13,018
Total Current Liabilities	(12,555)	13,018
Deferred credits and other long-term liabilities	(43,613)	46,999
Total Liabilities	(56,168)	60,017
Retained earnings	160	(145)
Total Stockholders' Equity	160	(145)
Total Liabilities and Stockholders' Equity	(56,008)	$ 59,872
ASU 2016-02 | Balance Without ASC 842 Adoption
Assets
Other long-term assets	34,989
Total Assets	3,015,149
LIABILITIES AND STOCKHOLDERS' EQUITY
Accrued liabilities	248,399
Total Current Liabilities	931,303
Deferred credits and other long-term liabilities	37,409
Total Liabilities	1,721,599
Retained earnings	1,419,895
Total Stockholders' Equity	1,293,550
Total Liabilities and Stockholders' Equity	$ 3,015,149