Variable Interest Entities - Additional Information (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Variable Interest Entities [Line Items]
Total assets of VIEs	$ 870,314
Total liabilities of VIEs	475,143
DMG | Discontinued Operations, Held-for-sale
Variable Interest Entities [Line Items]
Total assets of VIEs	595,670
Total liabilities of VIEs	$ 319,777