Long Term Debt - Additional information (Detail) (USD $)	3 Months Ended		6 Months Ended							1 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Including Acquisition Bridge Debt	Jun. 30, 2012 Excluding Acquisition Bridge Debt	Jun. 30, 2012 Minimum Unrestricted Cash Reduction	Jun. 30, 2012 Maximum	Jun. 30, 2012 Maximum Unrestricted Cash Reduction	Apr. 30, 2012 AR Credit Facility	Jun. 30, 2012 Revolving Facility	Jun. 30, 2012 6.25% Senior Notes, Due 2037	Jan. 23, 2012 6.25% Senior Notes, Due 2037	Jun. 30, 2012 6.6% Senior Notes, due 2018	Jun. 30, 2012 6.6% Senior Notes, due 2018
Debt Instrument
Senior notes debt outstanding repurchased after year end												$ 20,000,000
Percent of par value paid to repurchase senior notes													$ 90.75
Revolving credit facility borrowings to finance repurchase of senior notes after year end												18,200,000
Debt instrument maturity date										April 20, 2013		2037		2018	2018
Interest rate on notes												6.25%		6.60%	6.60%
Debt covenant			The Credit Agreement (which consists of the Term Loan Facility and a $350,000,000 Revolving Facility) and the AR Credit Facility require the Corporation’s ratio of consolidated debt to consolidated earnings before interest, taxes, depreciation, depletion and amortization (EBITDA), as defined, for the trailing twelve month period (the “Ratio”) to not exceed 3.50x as of the end of any fiscal quarter, provided that the Corporation may exclude from the Ratio debt incurred in connection with certain acquisitions for a period of 180 days so long as the Corporation maintains specified ratings on its long-term unsecured debt and the Ratio calculated without such exclusion does not exceed 3.75x. Additionally, if no amounts are outstanding under both the Revolving Facility and the AR Credit Facility, consolidated debt, including debt guaranteed by the Corporation, may be reduced by the Corporation’s unrestricted cash and cash equivalents in excess of $50,000,000, such reduction not to exceed $200,000,000, for purposes of the covenant calculation.		3.50	3.75		3.95
Reduction of consolidated debt in the debt ratio calculation							50,000,000
Maximum consolidated debt reduction for unrestricted cash and cash equivalents for debt covenant calculation									200,000,000
Line of Credit facility, Borrowing capacity											350,000,000
Outstanding letters of credit reducing line of credit borrowing capacity	2,507,000		2,507,000
Additional interest expense	257,000	239,000	508,000	474,000
Increase in annual interest expense due to ongoing amortization of the terminated value of the swap agreements														$ 1,000,000	$ 1,000,000