Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Loss Contingencies [Line Items]
Rent expense under cancelable and non-cancelable operating leases	$ 0.9	$ 0.8	$ 1.9	$ 1.7
Deposits as collateral for outstanding surety bonds	0.0		0.0		$ 0.5
Outstanding performance and surety bonds	174.3		174.3
Non-refundable deposits	65.0		65.0
Remaining purchase price of land	456.9		456.9
Project construction commitment
Loss Contingencies [Line Items]
Other commitment	$ 277.0		$ 277.0