Basis and Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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	$ (535,000)	$ 446,000	(1,012,000)	$ 649,000
Ending balance	1,744,813,000		1,744,813,000
Foreign Currency
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			774,000
Other Comprehensive Loss			(1,012,000)
Ending balance	$ (238,000)		$ (238,000)