Basis and Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 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	$ 297,000	$ 782,000	(715,000)	$ 1,431,000
Ending balance	1,763,506,000		1,763,506,000
Foreign Currency
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			774,000
Other Comprehensive Loss			(715,000)
Ending balance	$ 59,000		$ 59,000