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Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Interest paid	$ 14,545,000	$ 11,216,000
Interest expense on debt to related parties	1,612,000	$ 2,627,000
Softbank Corp.
Related Party Transaction [Line Items]
Accounts receivable	2,700,000		$ 2,400,000
Consulting Agreement \| General Colin L. Powell \| Director
Related Party Transaction [Line Items]
Related party amount of transaction	125,000
PPA Company IIIa
Related Party Transaction [Line Items]
Repayments of debt	5,209,000		$ 4,431,000
PPA Company IIIa \| Term loan \| Term Loan due September 2028, Non-Recourse \| Affiliated entity
Related Party Transaction [Line Items]
Repayments of debt	800,000
Interest paid	$ 800,000