Goodwill and Other Intangibles - Changes in the carrying amount of goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance at beginning of year	$ 182,012	$ 179,792
Translation adjustments	5,231	2,220
Balance at end of year	$ 187,243	$ 182,012