Summary of Significant Accounting Policies - Contract Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Changes in the Company's contract assets and contract liabilities
Contract asset, Beginning balance	$ 500
Contract asset, Additions	8,000	$ (500)
Contract asset, Deductions	(500)	(5,000)
Contract Asset, Impact Of Netting.	(4,369)	5,000
Contract asset, Ending balance	3,631	500
Contract liabilities:
Contract liabilities, Beginning balance	80,802	89,967
Contract liabilities, Additions	65,816	730
Contract liabilities, Deductions	(14,817)	(14,895)
Contract Liabilities, Impact Of Netting	(4,369)	5,000
Contract liabilities, Ending balance	$ 127,432	$ 80,802