Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Investment in partnership	$ 93,089	$ 22,601
Net operating loss carryforwards	21,283	5,949
Deferred tax assets	114,372	28,550
Less: valuation allowance	0	0
Deferred tax assets, net of valuation allowance	114,372	28,550
Deferred tax liabilities:
Other	0	0
Deferred tax liabilities	0	0
Net deferred tax assets	$ 114,372	$ 28,550