Debt - Narrative (Details)		9 Months Ended	12 Months Ended
	Oct. 22, 2015 USD ($) entity	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 22, 2016 USD ($)	Feb. 25, 2016 USD ($)	Aug. 11, 2015 USD ($)	Dec. 12, 2014 USD ($)
Debt Instrument [Line Items]
Term to determine contractual rate			360 days
Weighted average interest rate (percent)		3.04%
Term to determine weighted average rate		365 days
Number of wholly owned SPE | entity	6
Long-term debt		$ 471,568,000	$ 456,472,000
Key Bank Credit Facility | Line of Credit
Debt Instrument [Line Items]
Contractual interest rate		2.74%
Weighted average interest rate (percent)		2.78%
Term of loan		4 years
Revolving credit facility, extension term		1 year
AIG Loan | Notes Payable, Other Payables
Debt Instrument [Line Items]
Contractual interest rate		4.15%
Duration monthly payments of interest only		5 years
Long-term debt	$ 127,000,000
Revolving Credit Facility | Key Bank Credit Facility
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity				$ 550,000,000		$ 410,000,000.0	$ 250,000,000.0
Revolving credit facility, maximum borrowing capacity							$ 1,250,000,000.00
Revolving Credit Facility | U.S. Bank Facility
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity				$ 50,000,000
London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis rate (percent)		1.24%
London Interbank Offered Rate (LIBOR) | Key Bank Credit Facility | Line of Credit
Debt Instrument [Line Items]
Basis spread on variable rate (percent)		1.50%
Interest Rate Swap
Debt Instrument [Line Items]
Notional amount		$ 100,000,000.0			$ 100,000,000.0