Business Acquisition - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$ 62,030	$ 61,888	$ 60,470	$ 2,520
Octane Fitness
Business Acquisition [Line Items]
Cash	7,759
Accounts receivable	12,476
Inventories	13,134
Prepaid expenses	885
Deferred tax assets	1,303
Property, plant and equipment	3,372
Intangible assets	63,100
Total assets acquired	102,029
Accounts payable	6,497
Accrued liabilities	2,968
Warranty obligations	5,550
Deferred tax liabilities, non-current	21,033
Other non-current liabilities	390
Total liabilities assumed	36,438
Net identifiable assets acquired	65,591
Goodwill	59,705
Net assets acquired	$ 125,296