Borrowing Arrangements - Additional Information (Details)		7 Months Ended	12 Months Ended			41 Months Ended
	Feb. 20, 2015 USD ($)	Sep. 30, 2015	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)	Sep. 30, 2016	Feb. 20, 2020	Oct. 02, 2012 USD ($)
Debt Instrument [Line Items]
Discount on debt			$ 800,000
Redemption value of convertible debentures outstanding			$ 1,100,000	$ 1,100,000
Restated Credit Facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Weighted average interest rate on senior credit facility (as a percentage)			3.30%	3.00%
Convertible Debentures
Debt Instrument [Line Items]
Redemption price (in dollars per share) | $ / shares			$ 19.18
Debt redemptions			$ 0
Senior Credit Facility | Restated Credit Facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 450,000,000
Weighted average interest rate on senior credit facility (as a percentage)			2.90%	2.80%
Senior Credit Facility | Revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity							200,000,000
Senior Credit Facility | Letter of credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity							100,000,000
Senior Credit Facility | Term loan facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 250,000,000.0						$ 250,000,000
Restated Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	400,000,000.0
Losses on the extinguishment of debt related to debt discount and debt issuance costs	600,000
Restated Credit Agreement | Restated Credit Facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Maximum borrowing capacity	200,000,000.0
Current borrowing capacity			$ 148,700,000
Letters of credit outstanding			48,500,000
Borrowings excluding debt discount			152,800,000
Discount on debt			800,000
Deferred financing cost			1,000,000
Restated Credit Agreement | Revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity	100,000,000.0
Outstanding borrowing	147,300,000
Restated Credit Agreement | Letter of credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity	100,000,000.0
Outstanding borrowing	53,400,000
Restated Credit Agreement | Term loan facility
Debt Instrument [Line Items]
Maximum borrowing capacity	200,000,000.0
Amount drawn	10,400,000
Year one amortization of principal	15,000,000.0
Year two amortization of principal	15,000,000.0
Year three amortization of principal	20,000,000.0
Year four amortization of principal	20,000,000.0
Year five amortization of principal	20,000,000.0
Year six amortization of principal	110,000,000.0
Restated Credit Agreement | Swingline Loans
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000,000.0
Restated Credit Agreement | Maximum | Restated Credit Facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Total debt to EBITDA ratio that is required to be maintained (less than)		4.0			3.75
Restated Credit Agreement | Maximum | Restated Credit Facility, net of original discount on borrowings and deferred financing costs | Forecast
Debt Instrument [Line Items]
Total debt to EBITDA ratio that is required to be maintained (less than)						3.5
Restated Credit Agreement | Minimum | Restated Credit Facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Fixed charge coverage ratio that is required to be maintained	1.25
Restated Credit Agreement | LIBOR Loans | Restated Credit Facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Period of total debt to EBITDA ratio	12 months
Restated Credit Agreement | Base rate loans | Restated Credit Facility, net of original discount on borrowings and deferred financing costs | Base Rate
Debt Instrument [Line Items]
Interest rate margin on variable rate basis (as a percentage)	0.50%
Restated Credit Agreement | Base rate loans | Restated Credit Facility, net of original discount on borrowings and deferred financing costs | LIBOR
Debt Instrument [Line Items]
Interest rate margin on variable rate basis (as a percentage)	1.00%
Restated Credit Agreement | Credit Agreement | Restated Credit Facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 148,700,000