Goodwill and Intangible Assets - Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Balance at beginning of period	$ 305,238
Preliminary purchase price allocations for acquisitions	17,267
Effect of foreign currency translation adjustments	(510)
Balance at end of period	$ 321,995