Long-term Obligations - Fan Pier Leases (Details) $ in Thousands, ft² in Millions	12 Months Ended
	Dec. 31, 2011 ft² lease building	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Property and equipment, net		$ 759,978	$ 698,362
Fan Pier Leases
Property, Plant and Equipment [Line Items]
Number of leases | lease	2
Area of real estate property (in square feet) | ft²	1.1
Number of buildings under lease agreement | building	2
Optional term of lease agreement (in years)	10 years
Fan Pier Leases | Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, net		479,000	489,000
Fan Pier Leases | Buildings
Property, Plant and Equipment [Line Items]
Construction financing lease obligation, current and noncurrent		$ 472,200	$ 472,600