Commitments and contingencies (Litigation and Claims) (Details) - USD ($) $ in Thousands					12 Months Ended
	Apr. 20, 2017	Mar. 21, 2017	Jan. 17, 2017	Aug. 15, 2016	Dec. 31, 2019
Class A
Loss Contingencies [Line Items]
Common stock issued upon settlement (in shares)		37,110,630			84,347
Naylor Farms Case Putative Class Action | Low | Pending Litigation
Loss Contingencies [Line Items]
Damages sought				$ 150,000	$ 5,000
Naylor Farms Case
Loss Contingencies [Line Items]
Minimum percentage of plaintiff in modified class			60.00%
Naylor Farms Case Actual and Putative Action | Low | Pending Litigation
Loss Contingencies [Line Items]
Damages sought	$ 90,000
W.H. Davis Case
Loss Contingencies [Line Items]
Damages sought					17,262
W.H. Davis Case | Davis
Loss Contingencies [Line Items]
Amount of claims					$ 2,650