Fair Value Measurements - Change in Redeemable Noncontrolling Interests (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Redeemable Noncontrolling Interests [Roll Forward]
Balance at beginning of period	$ 151,978	$ 45,755
Addition to redeemable noncontrolling interest		277
Redemption of redeemable noncontrolling interest	(11,536)
Net income (loss) attributable to redeemable noncontrolling interest	1,184	(4,905)
Adjustment of the redeemable noncontrolling interest to fair value	12,011	108,296
Effect of foreign currency translation attributable to redeemable noncontrolling interest	1,612	2,555
Balance at end of period	$ 155,249	$ 151,978