Acquisitions and Other Recent Business Ventures - Plainridge Racecourse Acquisition (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquisitions
Payments of contingent purchase price			$ 19,613	$ 1,807
Plainridge Racecourse
Acquisitions
Period over which contingent consideration payments are due			10 years
Period contingent purchase price consideration is due following first four fiscal quarters			60 days
Period for yearly contingent purchase price consideration payment after the first payment			9 years
Fair value of contingent purchase price consideration			$ 21,300	10,700	$ 13,800
Payments of contingent purchase price	$ 2,000	$ 1,800
General and administrative expenses | Plainridge Racecourse
Acquisitions
Gain (loss) on change in long-term debt fair value			$ (12,500)	$ 1,300	$ 5,400