Summary of Significant Accounting Policies - Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting
Number of operating segments									1
Maximum percentage of net sales outside North America									1.00%
Net sales	$ 100,054	$ 78,836	$ 88,225	$ 36,396	$ 72,997	$ 52,026	$ 55,156	$ 14,141	$ 303,511	$ 194,320	$ 140,033
Equipment
Segment Reporting
Net sales									254,234	164,460	123,308
Parts and accessories
Segment Reporting
Net sales									$ 49,278	$ 29,860	$ 16,725