Summary of Significant Accounting Policies - Contract Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Changes in the Company's contract assets and contract liabilities
Contract asset, Beginning balance	$ 3,631	$ 500
Contract asset, Additions		0
Contract asset, Deductions	3,000	500
Contract Asset, Impact Of Netting.	359
Contract asset, Ending balance	990
Contract liabilities:
Contract liabilities, Beginning balance	127,432	80,802
Contract liabilities, Additions		65,287
Contract liabilities, Deductions	(283)	(79)
Contract Liabilities, Impact Of Netting	361
Contract liabilities, Ending balance	$ 127,510	$ 146,010