Related party transactions (Details)	1 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2014 USD ($) Automobile	Sep. 30, 2015 USD ($)	Dec. 31, 2016 USD ($) Device	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jun. 30, 2013 USD ($)
Chief Executive Officer (CEO) [Member] | Related Party Transaction, Chartered Aircraft Expenses [Member]
Related Party Transaction [Line Items]
Expense for services rendered			$ 500,000	$ 700,000	$ 600,000
Accounts payable to related party			0	100,000
Chief Executive Officer (CEO) [Member] | Related Party Transaction, Automobiles Purchased [Member]
Related Party Transaction [Line Items]
Number of automobiles purchased by related party | Automobile	7
Revenue from related parties	$ 300,000
Immediate Family Member of Member of the Board [Member]
Related Party Transaction [Line Items]
Naming rights agreement, period						3 years
Payments to be made to related party for naming rights						$ 600,000
Aggregate payments to related party for naming rights			$ 600,000
Number of devices provided to related party at no cost | Device			100
Company Affiliated with Investors [Member] | Related Party Transaction, Contract Manufacturing Agreement [Member]
Related Party Transaction [Line Items]
Expense for services rendered		$ 0
Accounts payable to related party			$ 0	0
Payments to related party vendor			0	$ 200,000	$ 12,200,000
Director [Member]
Related Party Transaction [Line Items]
Expense for services rendered			400,000
Accounts payable to related party			$ 300,000
Executive Officer [Member] | Related Party Transaction, Demand Payment Loan [Member]
Related Party Transaction [Line Items]
Loan amount to executive officer pursuant to demand loan payment							$ 200,000