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Debt Disclosure [Line Items]

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Debt Instrument Offer Price Percentage

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Debt Redemption Price Percent Of Principal Amount

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Debt To Capitalization Ratio

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Interest Coverage ratio

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Line of Credit Facility, Additional Borrowing Capacity

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Percentage of repurchase price to principal debt amount

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Principal payments, percentage

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The component of interest expense comprised of the periodic charge against earnings over the life of the financing arrangement to which such costs relate. Alternate captions include Noncash Interest Expense.

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Description of minimum financial levels (for example, tangible net worth and working capital) and achievement of certain financial ratios (for example, working capital ratio and debt service coverage ratio), and adherence to certain clauses which generally require or restrict certain actions (for example, entering into a debt arrangement with equal or greater seniority, and selling or discontinuing a certain business segment or material subsidiary) to be in compliance with the covenant clauses of the debt agreement. May also include a discussion of the adverse consequences that would result if the entity violates or fails to satisfy the covenants.

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Date that the debt agreement requires the first payment to be made, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

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The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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Interest rate stated in the contractual debt agreement.

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Date when the debt instrument was issued, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

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Date when the debt instrument is scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount borrowed under the credit facility as of the balance sheet date.

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Description of the conditions for borrowing under the credit facility including the nature of any restrictions.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Description of the frequency of the required periodic payments of interest, principal, or both, and the amount, if set, or a description of a formula upon which payment is based.

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Description of the frequency of periodic payments, which may be presented in a variety of ways (for example, monthly, quarterly, annually).

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Reflects when the credit facility first became available, which may be presented in a variety of ways (year, month and year, day, month and year, quarter).

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The effective interest rate at the end of the reporting period.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

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The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

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The cash outflow to pay off an obligation from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with either short term or long term maturity.

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Long Term Debt - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended					1 Months Ended		1 Months Ended									1 Months Ended
	Oct. 05, 2010	Jun. 30, 2011	Oct. 31, 2010	Jun. 30, 2011	Aug. 19, 2010 2010 Credit Agreement LegalMatter	Jun. 30, 2011 2010 Credit Agreement	Aug. 19, 2010 2010 Credit Agreement Revolving Credit Facility	Jun. 30, 2011 2010 Credit Agreement Revolving Credit Facility	Jun. 30, 2011 2010 Credit Agreement Revolving Credit Facility Letter of Credit	Aug. 19, 2010 2010 Credit Agreement Revolving Credit Facility Letter of Credit	Aug. 19, 2010 2010 Credit Agreement Revolving Credit Facility Bridge Loan	Aug. 19, 2010 2010 Credit Agreement Term Loan Facility	Jun. 30, 2011 2010 Credit Agreement Term Loan Facility	Aug. 19, 2010 2010 Credit Agreement Term Loan Facility First Four Quarterly Installments	Aug. 19, 2010 2010 Credit Agreement Term Loan Facility Subsequent Eight Quarterly Installments	Aug. 19, 2010 2010 Credit Agreement Term Loan Facility Next Subsequent Three Quarterly Installments	Jun. 30, 2011 2010 Credit Agreement LIBOR	Aug. 19, 2010 2010 Credit Agreement LIBOR Minimum	Aug. 19, 2010 2010 Credit Agreement LIBOR Maximum	Jun. 30, 2011 2010 Credit Agreement Base Rate	Aug. 19, 2010 2010 Credit Agreement Base Rate Minimum	Aug. 19, 2010 2010 Credit Agreement Base Rate Maximum	Aug. 19, 2010 2010 Credit Agreement Minimum Point	Aug. 19, 2010 2010 Credit Agreement Maximum	Oct. 05, 2010 Series A, Senior Notes, 4.97 Percent, Due October 5th 2020 LegalMatter	Oct. 05, 2010 Series A, Senior Notes, 4.97 Percent, Due October 5th 2020 Semi Annual Payment, First Payment	Oct. 05, 2010 Series A, Senior Notes, 4.97 Percent, Due October 5th 2020 Semi Annual Payment, Second Payment	Oct. 05, 2010 Series A, Senior Notes, 4.97 Percent, Due October 5th 2020 Minimum Point	Oct. 05, 2010 Series A, Senior Notes, 4.97 Percent, Due October 5th 2020 Maximum
Debt Disclosure [Line Items]
Credit agreement date					2010-08-19
Current aggregate borrowing capacity							$ 400,000,000			$ 150,000,000	$ 40,000,000
Notes isuance date																									2010-10-05
Aggregate amount by which the revolving credit facility can be increased							100,000,000
Long-term debt, aggregate principal amount																									300,000,000
Debt interest rate																									4.97%
Debt maturity date							Aug. 19, 2013					Aug. 19, 2014													Oct. 05, 2020
Credit facility, maximum borrowing capacity							500,000,000
Line of credit												100,000,000
Line of credit facility, frequency of payment and payment terms												The term loan facility is payable in quarterly principal installments commencing November 19, 2010., The installment amounts vary from 1.25% of the original principal amount for each of the first four quarterly installments, 2.50% of the original principal amount for each of the subsequent eight quarterly installments, 5.00% of the original principal amount for the next subsequent three quarterly installments, with the remainder becoming due at maturity.
Line of credit facility, frequency of payments												quarterly
Commencement date of interest payments												2010-11-19													2011-04-05
Description of the prepayment terms																									The Notes are prepayable at the Company's option, in whole or in part, provided that in the case of a partial prepayment, prepayment must be in an amount not less than 5% of the aggregate principal amount of the Notes then outstanding, at any time and from time to time at 100% of the principal amount prepaid, plus accrued and unpaid interest to the prepayment date
Installment amounts percentage of the original principal amount														1.25%	2.50%	5.00%												5.00%
Applicable margin																	2.75%	2.75%	3.75%	1.75%	1.75%	2.75%
Commitment fee payable to the lenders for the unused portion of the revolving credit facility						0.50%																	0.50%	0.75%
Financial covenant description																									The Company must not permit its debt to capitalization ratio to exceed 50% at any time. The note purchase agreement generally defines the debt to capitalization ratio as the ratio of (a) total borrowed money indebtedness to (b) the sum of such indebtedness plus consolidated net worth, with consolidated net worth determined as of the last day of the most recently ended fiscal quarter. The Company also must not permit the interest coverage ratio as of the last day of a fiscal quarter to be less than 2.50 to 1.00. The note purchase agreement generally defines the interest coverage ratio as the ratio for the four prior quarters of EBITDA to interest charges for that same period.
Financial covenant description					The Company must not permit its debt to capitalization ratio to exceed 45% at any time. The 2010 Credit Agreement generally defines the debt to capitalization ratio as the ratio of (a) total borrowed money indebtedness to (b) the sum of such indebtedness plus consolidated net worth, with consolidated net worth determined as of the last day of the most recently ended fiscal quarter. The Company also must not permit the interest coverage ratio as of the last day of a fiscal quarter to be less than 3.00 to 1.00. The 2010 Credit Agreement generally defines the interest coverage ratio as the ratio of earnings before interest, taxes, depreciation and amortization ("EBITDA") of the four prior fiscal quarters to interest charges for the same period.
Number of compliance covenants					2																				2
Debt to capitalization ratio, percentage the Company must not exceed at any time																								45.00%					50.00%
Interest coverage ratio that the Company must exceed on the last day of the fiscal quarter																							3.00					2.50
Line of credit, amount outstanding													96,300,000
Line of credit, interest rate													3.125%
Unfunded letters of credit, amount outstanding		40,600,000		40,600,000					40,600,000
Line of credit, available borrowing capacity								359,000,000
Repayment of revolving credit facility	200,000,000
Debt price as a percentage of principal amount																									100.00%
Prepayment terms, percent of principal before accrued and unpaid interest and "make-whole" premium																									100.00%
Description of the acceptance terms																									If any offer to prepay is accepted, the purchase price of each prepaid Note is 100% of the principal amount thereof, plus accrued and unpaid interest thereon to the prepayment date.
Acceptance terms, percent of principal before accrued and unpaid interest																									100.00%
Interest pay date																										April 5	October 5
Debt issuance costs			10,800,000
Interest expense related to amortization of debt issuance costs		$ 604,000		$ 1,200,000