Borrowing Arrangements - Additional Information (Details)		12 Months Ended
	Feb. 20, 2015 USD ($)	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Nov. 30, 2018 USD ($)
Debt Instrument [Line Items]
Redemption value of convertible debentures outstanding		$ 1,100,000	$ 1,100,000
Credit facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Amount of senior credit facility aggregated		$ 386,700,000
Weighted average interest rate on senior credit facility (as a percentage)		4.30%	3.30%
Convertible Debentures
Debt Instrument [Line Items]
Redemption price (in dollars per share) | $ / shares		$ 19.18
Debt redemptions		$ 0	$ 0
Restated Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 400,000,000.0			$ 550,000,000
Percentage of scheduled quarterly amortization		1.25%
Restated Credit Agreement | Credit facility, net of original discount on borrowings and deferred financing costs
Debt Instrument [Line Items]
Maximum borrowing capacity	200,000,000.0	$ 174,800,000.0		325,000,000
Letters of credit outstanding		$ 51,100,000
Restated Credit Agreement | Letter of credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity	100,000,000.0			100,000,000
Restated Credit Agreement | Term loan facility
Debt Instrument [Line Items]
Maximum borrowing capacity	200,000,000.0			$ 225,000,000
Restated Credit Agreement | Swingline Loans
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000,000.0
Restated Credit Agreement | Maximum | 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)	4.25
Restated Credit Agreement | Minimum | 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	3.50
Restated Credit Agreement | LIBOR Loans | 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 | 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 | 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%
Senior Credit Facility | 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)		4.00%	2.90%