Variable Interest Entities - Additional Information (Details) $ in Thousands	Dec. 31, 2018 USD ($) entity	Dec. 31, 2017 USD ($)
Variable Interest Entity [Line Items]
Number of consolidated entities | entity	4
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum exposure to loss in unconsolidated VIEs	$ 230,000
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum exposure to loss in unconsolidated VIEs	$ 568,272	$ 346,097