Debt - Additional Information (Detail)	1 Months Ended				3 Months Ended
	Nov. 17, 2017 USD ($)	Sep. 26, 2017 USD ($)	May 31, 2012 USD ($)	Apr. 30, 2012 USD ($)	Mar. 31, 2018 USD ($) $ / shares	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 27, 2017 USD ($)
Debt Instrument [Line Items]
Liquidity Position To Meet Future Obligations, Amount					$ 322,200,000
Interest expense					7,454,000	$ 2,990,000
Gains (losses) on extinguishment of debt, total					(174,000)	(640,000)
Amortization of Debt Issuance Costs and Discounts					100,000	100,000
Shareholders' Equity
Debt Instrument [Line Items]
Debt instrument, repurchase amount					9,200,000
Debt instrument, repurchased face amount					17,200,000
Gains (losses) on extinguishment of debt, total					200,000
Convertible Senior Notes
Debt Instrument [Line Items]
Notes issued, aggregate principal amount				$ 150,000,000
Notes issued, interest rate				3.375%
Proceeds from Notes Payable				$ 145,100,000
Debt Instrument Convertible Conversion Amount Settled Over the Principal					$ 63,000,000
Convertible Senior Notes | Walker Group Holdings LLC
Debt Instrument [Line Items]
Debt Instrument Maturity Year				2018
Unsecured Debt
Debt Instrument [Line Items]
Notes initial conversion rate per 1,000 in principal amount					85.4372
Principal amount of notes conversation for 85.4372 shares of common stock					$ 1,000
Notes initial conversion price | $ / shares					$ 11.70
Unsecured Debt | Convertible Senior Notes
Debt Instrument [Line Items]
Notes issued, aggregate principal amount					$ 150,000,000
Estimated implied interest rate					7.00%
Fair value of liability component upon issuance					$ 123,800,000
Difference between cash proceeds before offering expenses and the estimated fair value of liability component					21,700,000
Proceeds from issuance of convertible senior notes					145,500,000
Debt Conversion, Converted Instrument, Amount					27,000,000
Amended Credit Agreement
Debt Instrument [Line Items]
Interest Paid					1,800,000	2,000,000
Gains (losses) on extinguishment of debt, total						600,000
Term Loan Credit Agreement Principal Amount					500,000	$ 500,000
Senior Notes [Member]
Debt Instrument [Line Items]
Notes issued, aggregate principal amount								$ 325,000,000
Notes issued, interest rate								5.50%
Notes issued, interest payment frequency		The Senior Notes bear interest at the rate of 5.50% per annum from the date of issuance, and will pay interest semi-annually in cash on April 1 and October 1 of each year, beginning on April 1, 2018.
Fair value of liability component upon issuance					319,522,000		$ 319,377,000
Credit facility, maturity date		Oct. 01, 2025
Interest expense					$ 4,600,000
Proceeds from Issuance of Senior Long-term Debt		$ 318,900,000
Debt Instrument, Redemption, Description		The Senior Notes will mature on October 1, 2025. At any time prior to October 1, 2020, the Company may redeem some or all of the Senior Notes for cash at a redemption price equal to 100% of the aggregate principal amount of the Senior Notes being redeemed plus an applicable make-whole premium set forth in the indenture for the Senior Notes and accrued and unpaid interest to, but not including, the redemption date. Prior to October 1, 2020, the Company may redeem up to 40% of the Senior Notes at a redemption price of 105.50% of the principal amount, plus accrued and unpaid interest to, but not including, the redemption date, with the proceeds of certain equity offerings so long as if, after any such redemption occurs, at least 60% of the aggregate principal amount of the Senior Notes remains outstanding. On and after October 1, 2020, the Company may redeem some or all of the Senior Notes at redemption prices (expressed as percentages of principal amount) equal to 102.750% for the twelve-month period beginning on October 1, 2020, 101.375% for the twelve-month period beginning October 1, 2021 and 100.000% beginning on October 1, 2022, plus accrued and unpaid interest to, but not including, the redemption date. Upon the occurrence of a Change of Control (as defined in the indenture for the Senior Notes), unless the Company has exercised its optional redemption right in respect of the Senior Notes, the holders of the Senior Notes have the right to require the Company to repurchase all or a portion of the Senior Notes at a price equal to 101% of the aggregate principal amount of the Senior Notes, plus any accrued and unpaid interest to, but not including, the date of repurchase.
Revolving Credit Facility
Debt Instrument [Line Items]
Credit facility, maturity date					Jun. 04, 2020
Debt Instrument, Description of Variable Rate Basis					The Revolving Credit Facility (i) bears interest, at the Borrowers’ election, at (x) LIBOR (subject to a floor of 0%) plus a margin ranging from 150 basis points to 200 basis points, or (y) a base rate plus a margin ranging from 50 basis points to 100 basis points, in each case, based upon the monthly average excess availability under the Revolving Credit Facility, (ii) requires the Company to pay a monthly unused line fee equal to 25 basis points times the average unused availability under the Revolving Credit Facility, (iii) provides that if availability under the Revolving Credit Facility is less than 12.5% of the total commitment under the Revolving Credit Facility or if there exists an event of default, amounts in any of the Borrowers’ and the subsidiary guarantors’ deposit accounts (other than certain excluded accounts) will be transferred daily into a blocked account held by the Agent and applied to reduce the outstanding amounts under the Revolving Credit Facility, and (iv) requires the Company to maintain a minimum fixed charge coverage ratio of not less than 1.1 to 1.0 as of the end of any period of 12 fiscal months when excess availability under the Revolving Credit Facility is less than 10% of the total commitment under the Revolving Credit Facility.
Line of Credit Facility, Borrowing Capacity, Description					an uncommitted accordion feature allowing for an increase to the availability under the revolving credit facility of up to $50 million, subject to certain conditions
Revolving Credit Facility | Senior Secured Credit Facility
Debt Instrument [Line Items]
Notes issued, aggregate principal amount			$ 175,000,000
Term Loan Credit Agreement
Debt Instrument [Line Items]
Percentage of tranche loan amount on equal quarterly installments	0.25%
Line of Credit Facility, Amount Outstanding					$ 187,100,000
Debt Instrument, Periodic Payment, Principal					$ 1,900,000
Term Loan Credit Agreement | Senior Secured Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	$ 188,000,000		$ 188,000,000
Debt Instrument, Description of Variable Rate Basis	(i) LIBOR (subject to a floor of 0%) plus a margin of 225 basis points or (ii) a base rate (subject to a floor of 0%) plus a margin of 125 basis points.
Debt Instrument, Description			an uncommitted accordion feature to provide for additional senior secured term loans of up to $75 million plus an unlimited amount provided that the senior secured leverage ratio would not exceed 3.00 to 1.00, subject to certain conditions
Term Loan Credit Agreement | Incremental Senior Credit Facility
Debt Instrument [Line Items]
Senior Secured Leverage Ratio					3.00 to 1.00
Minimum | Revolving Credit Facility | Amended and Restated Credit Agreement
Debt Instrument [Line Items]
Fixed Charge Coverage Ratio Minimum					1.0
Maximum | Revolving Credit Facility | Amended and Restated Credit Agreement
Debt Instrument [Line Items]
Fixed Charge Coverage Ratio Minimum					1.1