Commitments, contingencies and guarantees - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 3,300	$ 2,000	$ 8,200	$ 5,200
Current product warranty accrual	9,061		9,061		$ 6,000
Noncurrent product warranty accrual	$ 400		$ 400		$ 400