Commitments and Contingencies, Letters of Credit (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Letters of Credit Outstanding, Amount	$ 12,600,000	$ 9,400,000
Line of Credit Facility, Maximum Borrowing Capacity	50,000,000
Purchase Commitment, Remaining Minimum Amount Committed	$ 16,700,000
Maximum [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	81.63%
Minimum [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	16.63%