Debt - Term Loan - Narrative (Details)
9 Months Ended
Nov. 03, 2015
USD ($)
extension_option
Sep. 30, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Debt Instrument [Line Items]        
Unamortized deferred financing costs   $ 31,013,000 $ 37,111,000  
Term Loan        
Debt Instrument [Line Items]        
Total debt, gross $ 325,000,000   420,000,000 $ 370,000,000
Number of one-year extension options | extension_option 2      
Extension option, term (in years) 1 year      
Accordion feature, maximum borrowing capacity $ 600,000,000      
Days available to reborrow loans repaid 30 days      
Period subject to reborrowing occurrence limitations (in months) 12 months      
Origination costs $ 2,400,000      
Unamortized deferred financing costs   $ 900,000 $ 1,500,000  
Term Loan | LIBOR        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent)   1.35%    
Minimum | Term Loan | LIBOR        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent) 1.35%      
Minimum | Term Loan | Base Rate        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent) 0.35%      
Maximum | Term Loan | LIBOR        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent) 1.80%      
Maximum | Term Loan | Base Rate        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent) 0.80%      
Achievement of Two of Three Credit Ratings, S&P at least BBB-, Fitch at least BBB-, Moody's at least Baa3 | Minimum | Term Loan | LIBOR        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent) 0.90%      
Achievement of Two of Three Credit Ratings, S&P at least BBB-, Fitch at least BBB-, Moody's at least Baa3 | Minimum | Term Loan | Base Rate        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent) 0.00%      
Achievement of Two of Three Credit Ratings, S&P at least BBB-, Fitch at least BBB-, Moody's at least Baa3 | Maximum | Term Loan | LIBOR        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent) 1.75%      
Achievement of Two of Three Credit Ratings, S&P at least BBB-, Fitch at least BBB-, Moody's at least Baa3 | Maximum | Term Loan | Base Rate        
Debt Instrument [Line Items]        
Basis spread on variable rate (as a percent) 0.75%