Significant Accounting Policies (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Option to purchase noncontrolling interest impairment charge	$ 0	$ 0
Beginning Balance	62,886,000
Redemptions	(1,166,000)	0
Changes in redemption value	(5,965,000)
Ending Balance	54,345,000		$ 62,886,000
Redeemable Noncontrolling Interest
Significant Accounting Policies [Line Items]
Beginning Balance	62,886,000	$ 60,180,000	60,180,000
Redemptions	(8,858,000)		(910,000)
Granted	0		1,666,000
Changes in redemption value	375,000		1,498,000
Currency translation adjustments	(58,000)		452,000
Ending Balance	$ 54,345,000		$ 62,886,000