General - Impact of Adoption of ASC 842 on Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets
Other long-term assets	$ 107,431	$ 84,350	$ 24,530
Total Assets	3,077,791	3,038,928	2,979,056
LIABILITIES AND STOCKHOLDERS' EQUITY
Accrued liabilities	260,980	244,374	231,356
Total Current Liabilities	925,127	911,911	898,893
Deferred credits and other long-term liabilities	76,482	83,482	36,483
Total Liabilities	1,743,521	1,753,770	1,693,753
Retained earnings	1,433,348	1,419,304	1,419,449
Total Stockholders' Equity	1,334,270	1,285,158	1,285,303
Total Liabilities and Stockholders' Equity	3,077,791	3,038,928	$ 2,979,056
Accounting Standards Update 2016-02 | Adjustments
Assets
Other long-term assets	(52,862)	59,820
Total Assets	(52,862)	59,872
LIABILITIES AND STOCKHOLDERS' EQUITY
Accrued liabilities	(11,700)	13,018
Total Current Liabilities	(11,700)	13,018
Deferred credits and other long-term liabilities	(41,398)	46,999
Total Liabilities	(53,098)	60,017
Retained earnings	236	(145)
Total Stockholders' Equity	236	(145)
Total Liabilities and Stockholders' Equity	(52,862)	$ 59,872
Accounting Standards Update 2016-02 | Balance Without ASC 842 Adoption
Assets
Other long-term assets	54,569
Total Assets	3,024,929
LIABILITIES AND STOCKHOLDERS' EQUITY
Accrued liabilities	249,280
Total Current Liabilities	913,427
Deferred credits and other long-term liabilities	35,084
Total Liabilities	1,690,423
Retained earnings	1,433,584
Total Stockholders' Equity	1,334,506
Total Liabilities and Stockholders' Equity	$ 3,024,929