Summary of Significant Accounting Policies - Derivatives (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / derivative_instrument	Mar. 31, 2018	Dec. 31, 2018 $ / derivative_instrument
Guaranty Liability - MHHA Horsemen
Derivative [Line Items]
Derivative, Term of Contract	5 years 10 months 10 days	6 years 1 month 10 days
Derivative, Equity Value | $ / derivative_instrument	10.05		10.13
Derivative, Price Risk Option Strike Price | $ / derivative_instrument	27.50		27.50
Derivative Liability - bet365
Derivative [Line Items]
Derivative, Term of Contract	3 years 29 days	3 years 5 months 16 days
Derivative, Equity Value | $ / derivative_instrument	21.66		29.48
Derivative, Price Risk Option Strike Price | $ / derivative_instrument	20.00		20.00
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance as of December 31, 2018	$ 900
Balance as of March 31, 2019	$ 1,000
Contingent forward contract - bet365
Derivative [Line Items]
Derivative, Term of Contract	2 years 9 months 4 days	3 years 1 month 17 days
Derivative, Equity Value | $ / derivative_instrument	21.66		29.48
Derivative, Price Risk Option Strike Price | $ / derivative_instrument	18.81		20.00
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance as of December 31, 2018	$ 1,900
Balance as of March 31, 2019	$ 100
Measurement Input, Price Volatility [Member] | Guaranty Liability - MHHA Horsemen
Derivative [Line Items]
Derivative Liability, Measurement Input	0.68		0.68
Measurement Input, Price Volatility [Member] | Derivative Liability - bet365
Derivative [Line Items]
Derivative Liability, Measurement Input	0.61		0.61
Measurement Input, Price Volatility [Member] | Contingent forward contract - bet365
Derivative [Line Items]
Derivative Asset, Measurement Input	0.61		0.62
Measurement Input, Risk Free Interest Rate [Member] | Guaranty Liability - MHHA Horsemen
Derivative [Line Items]
Derivative Liability, Measurement Input	0.022		0.026
Measurement Input, Risk Free Interest Rate [Member] | Derivative Liability - bet365
Derivative [Line Items]
Derivative Liability, Measurement Input	0.022		0.029
Measurement Input, Risk Free Interest Rate [Member] | Contingent forward contract - bet365
Derivative [Line Items]
Derivative Asset, Measurement Input	0.022		0.029
Measurement Input, Expected Dividend Rate [Member] | Guaranty Liability - MHHA Horsemen
Derivative [Line Items]
Derivative Liability, Measurement Input	0.000		0.000
Measurement Input, Expected Dividend Rate [Member] | Derivative Liability - bet365
Derivative [Line Items]
Derivative Liability, Measurement Input	0.000		0.000
Measurement Input, Expected Dividend Rate [Member] | Contingent forward contract - bet365
Derivative [Line Items]
Derivative Asset, Measurement Input	0.000		0.000
Fair Value, Inputs, Level 3 [Member] | Derivative Liability - bet365
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance as of December 31, 2018	$ 879
Change in fair value	(115)
Balance as of March 31, 2019	994
Fair Value, Inputs, Level 3 [Member] | Contingent forward contract - bet365
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance as of December 31, 2018	1,865
Change in fair value	1,761
Balance as of March 31, 2019	$ 104