Income Taxes - Additional Information (Details) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended	36 Months Ended
	Jun. 30, 2019 USD ($) solar_generator_unit	Mar. 31, 2019 fund	Jun. 30, 2019 USD ($) solar_generator_unit	Dec. 31, 2018 USD ($) fund	Dec. 31, 2015 USD ($) fund tax_opinion
Income Tax Disclosure [Abstract]
Number of federal renewable energy tax credit funds | fund		3		3	3
Number of solar generator units | solar_generator_unit	512		512
Federal tax credit benefit					$ 22,800
Number of tax opinions | tax_opinion					2
Tax credit recognized and measured for each tax position (as a percent)			100.00%
Percentage of solar generator units positively identified (over)			93.00%
Increase to the provision for income taxes	$ 223		$ 12,300
Estimated loss on the related tax positions			29,400
Uncertain tax position, accrued interest	$ 2,100		$ 2,100	$ 1,800