Basis and Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification out of accumulated other comprehensive income (loss)	$ 0
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	1,728,004,000
Other Comprehensive Loss	(477,000)	$ 203,000
Ending balance	1,756,192,000
Foreign Currency
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	774,000
Other Comprehensive Loss	(477,000)
Ending balance	$ 297,000