Noncontrolling Interest - Contributions (Details) - USD ($) $ in Thousands	6 Months Ended	9 Months Ended	12 Months Ended	15 Months Ended	36 Months Ended
	Dec. 31, 2017	Mar. 31, 2015	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Ownership percentage	100.00%	72.00%	92.00%	83.00%	100.00%
ASTC Contribution
Noncontrolling Interest [Line Items]
Contributions made	$ 3,500	$ 1,422	$ 3,000	$ 1,000	$ 8,922
Minority Owner
Noncontrolling Interest [Line Items]
Contributions made	$ (422)	$ 422	$ 0	$ 0	$ 0