Income Taxes - Significant Components of The Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Accruals and prepaids	$ 18,871	$ 14,387
Deferred revenue	0	7,602
Net operating loss carryforwards	288,039	187,038
Stock-based compensation	5,681	4,994
Investment tax and other credits	28,551	22,940
Interest Expense	9,614	0
Interest rate derivatives	1,282	1,640
Total deferred tax assets	352,038	238,601
Less: Valuation allowance	(10,506)	(2,892)
Gross deferred tax assets	341,532	235,709
Deferred tax liabilities
Deferred revenue	17,526	0
Capitalized initial direct costs	54,823	38,751
Fixed asset depreciation	218,701	173,175
Deferred tax on investment in partnerships	144,115	106,902
Gross deferred tax liabilities	435,165	318,828
Net deferred tax liabilities	$ (93,633)	$ (83,119)