Organization and Significant Accounting Policies - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	$ (1,568)
Foreign currency translation adjustments	800	$ (12)	$ (1,108)
Balance, end of period	(768)	(1,568)
Foreign currency translation
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	(1,574)	(1,568)
Foreign currency translation adjustments	802	(6)
Balance, end of period	(772)	(1,574)	(1,568)
Available-for-sale marketable securities
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	6	12
Net unrealized holding (loss)	(2)	(6)
Balance, end of period	4	6	$ 12
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	(1,568)
Balance, end of period	$ (768)	$ (1,568)