Goodwill (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2017 USD ($)
Goodwill [Line Items]
Highest goodwill balance among other reporting units			$ 5,675
Average goodwill balance among other reporting units			$ 840
Number of reporting units with allocated goodwill balances			221
Goodwill [Roll Forward]
Balance, beginning of period	$ 194,674	$ 182,027
Acquired goodwill	3,068	12,696
Goodwill, Translation Adjustments	1,572	(49)
Balance, end of period	199,314	194,674
Accumulated goodwill impairment losses	(9,879)	(9,266)
Goodwill impairment	0	(613)
Accumulated goodwill impairment losses	(9,879)	(9,879)
Goodwill	$ 189,435	$ 184,795