Summary of Significant Accounting Policies (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies [Abstract]
Foreign currency translation	$ (394,600)	$ (394,306)
Unrealized gains on investments	2,025	3,345
Estimated tax loss on unrealized gains on investments	(13)	(616)
Accumulated other comprehensive loss	$ (392,588)	$ (391,577)

Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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