Summary of Significant Accounting Policies Accounting Policies Warranty Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Warranty Costs [Abstract]
Warranty liability, beginning of period	$ 30,222	$ 35,634
Accrued warranty expense	17,760	17,368
Changes in estimates related to pre-existing warranties	1,453	4,701
Cost of warranty service work performed	(22,600)	(27,429)
Acquisitions	5,277	304
Foreign exchange translation effect	2,065	(356)
Warranty liability, end of period	$ 34,177	$ 30,222