Basis of Presentation and Significant Accounting Policies (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other current assets	$ 43,781		$ 74,203
Deferred income taxes	131,646		137,638
Retained earnings	$ 2,162,663		2,057,915
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption results			0
Accounting Standards Update 2018-02 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption results			6,435
Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption results			(645)
Other current assets		$ (7,300)
Deferred income taxes		6,700
Retained earnings		$ (600)
Accounting Standards Update 2016-16 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption results			(645)
Adjustments for New Accounting Pronouncement | Accounting Standards Update 2018-02 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption results			(6,400)
Adjustments for New Accounting Pronouncement | Accounting Standards Update 2018-02 | AOCI
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption results			$ 6,400