General - Cumulative Effect of Changes for Adoption of ASC 842 (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Leases
Change in Accounting Principle, Accounting Standards Update, Transition Option Elected	Modified Retrospective
Election of package of practical expedients	true
Operating lease right-of-use assets	$ 52,862
Assets
Deferred income taxes	3,212	$ 3,463	$ 3,411
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
Leases
Change in Accounting Principle, Accounting Standards Update, Adopted	true
Change in Accounting Principle, Accounting Standards Update, Early Adoption	false
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2019
New Accounting Pronouncement or Change in Accounting Principle, Prior Period Not Restated	true
Operating lease right-of-use assets		59,800
Lease liabilities		67,900
Accounting Standards Update 2016-02 | Adjustments
Assets
Deferred income taxes		52
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