Fair Value - Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Liabilities:
Participating preferred shares/units derivative liability	$ 68,469	$ 69,810	$ 65,730	$ 62,790
Recurring
Liabilities:
Participating preferred shares/units derivative liability	68,469	69,810
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Liabilities:
Participating preferred shares/units derivative liability	0	0
Recurring | Significant Other Observable Inputs (Level 2)
Liabilities:
Participating preferred shares/units derivative liability	0	0
Recurring | Significant Unobservable Inputs (Level 3)
Liabilities:
Participating preferred shares/units derivative liability	$ 68,469	$ 69,810