Common Stock, warrants, stock-based compensation, stock options, restricted stock and restricted stock units - Warrants (Details) - $ / shares			12 Months Ended
	Jul. 02, 2019	Jan. 30, 2018	Dec. 31, 2019
Number outstanding
Issued (in shares)		10,000
Weighted Average Exercise Price
Warrants And Rights, Exercised	66,041
Exercise of common stock warrants (in shares)	45,690
Outstanding warrants
Number outstanding
Outstanding at the beginning of the period (in shares)			76,041
Exercised (in shares)			(66,041)
Outstanding at the end of the period (in shares)			10,000
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)			$ 10.10
Exercised (in dollars per share)			10.90
Outstanding at the end of the period (in dollars per share)			$ 4.83
Obligation To Issue Warrants, In Shares			93,341