Long Term Debt - Additional Information (Detail) (USD $)	3 Months Ended			6 Months Ended		12 Months Ended	1 Months Ended		1 Months Ended						1 Months Ended			1 Months Ended																1 Months Ended				12 Months Ended
	Jun. 30, 2013	Sep. 30, 2012	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2010	Sep. 27, 2012 Credit Agreement LegalMatter	Jun. 30, 2013 Credit Agreement	Sep. 27, 2012 Credit Agreement First Four Quarterly Installments	Sep. 27, 2012 Credit Agreement Subsequent Eight Quarterly Installments	Sep. 27, 2012 Credit Agreement Subsequent Four Quarterly Installments	Sep. 27, 2012 Credit Agreement Amount For The Final Four Quarterly Installments	Sep. 27, 2012 Credit Agreement Revolving Credit Facility	Jun. 30, 2013 Credit Agreement Revolving Credit Facility	Sep. 27, 2012 Credit Agreement Term Loan Facility	Jun. 30, 2013 Credit Agreement Term Loan Facility	Sep. 27, 2012 Credit Agreement Minimum	Sep. 27, 2012 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 Minimum	Oct. 05, 2010 Series A, Senior Notes, 4.97 Percent, Due October 5th 2020 Maximum	Jun. 14, 2012 Series B, Senior Notes, 4.27 Percent, Due June 14th 2022 LegalMatter	Jun. 14, 2012 Series B, Senior Notes, 4.27 Percent, Due June 14th 2022 Minimum	Jun. 14, 2012 Series B, Senior Notes, 4.27 Percent, Due June 14th 2022 Maximum	Sep. 27, 2012 Letter of Credit Credit Agreement Revolving Credit Facility	Sep. 27, 2012 Swing Line Facility Credit Agreement Revolving Credit Facility	Sep. 27, 2012 Term Loan Credit Agreement Revolving Credit Facility	Jun. 30, 2013 London Interbank Offered Rate (LIBOR) Credit Agreement	Sep. 27, 2012 London Interbank Offered Rate (LIBOR) Credit Agreement Minimum	Sep. 27, 2012 London Interbank Offered Rate (LIBOR) Credit Agreement Maximum	Jun. 30, 2013 Base Rate Credit Agreement	Sep. 27, 2012 Base Rate Credit Agreement Minimum	Sep. 27, 2012 Base Rate Credit Agreement Maximum	Oct. 05, 2010 Semi Annual Payment, First Payment Series A, Senior Notes, 4.97 Percent, Due October 5th 2020	Jun. 14, 2012 Semi Annual Payment, First Payment Series B, Senior Notes, 4.27 Percent, Due June 14th 2022	Oct. 05, 2010 Semi Annual Payment, Second Payment Series A, Senior Notes, 4.97 Percent, Due October 5th 2020	Jun. 14, 2012 Semi Annual Payment, Second Payment Series B, Senior Notes, 4.27 Percent, Due June 14th 2022	Dec. 31, 2012 Credit Agreement Series B, Senior Notes, 4.27 Percent, Due June 14th 2022
Debt Disclosure [Line Items]
Current aggregate borrowing capacity													$ 500,000,000												$ 150,000,000	$ 40,000,000	$ 100,000,000
Line of credit facility, frequency of payment and payment terms															The term loan facility is payable in quarterly principal installments, which commenced December 27, 2012. 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 subsequent four quarterly installments and 13.75% of the original principal amount for the final four quarterly installments.
Line of credit facility, frequency of payments							Quarterly
Commencement date of principal payments							Dec. 27, 2012
Installment amounts percentage of the original principal amount									1.25%	2.50%	5.00%	13.75%
Aggregate amount by which the revolving credit facility can be increased													100,000,000
Credit facility, maximum borrowing capacity							700,000,000
Debt maturity date													Sep. 27, 2017						Oct. 05, 2020			Jun. 14, 2022
Applicable margin																												2.25%	2.25%	3.25%	1.25%	1.25%	2.25%
Commitment fee payable to the lenders for the unused portion of the credit facility							0.50%
Financial covenant description							The Company must not permit its debt to capitalization ratio to exceed 45%. The 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 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. The Company was in compliance with these covenants at June 30, 2013.
Number of compliance covenants							2												2			2
Debt to capitalization ratio, percentage the Company must not exceed at any time																		45.00%			50.00%			50.00%
Interest coverage ratio that the Company must exceed on the last day of the fiscal quarter																	300.00%			250.00%			250.00%
Line of credit, amount outstanding														0		96,300,000
Line of credit facility, interest rate																2.625%
Unfunded letters of credit, amount outstanding	39,800,000			39,800,000				39,800,000
Line of credit, available borrowing capacity								460,000,000
Notes issuance date																			Oct. 05, 2010			Jun. 14, 2012
Long-term debt, aggregate principal amount																			300,000,000			300,000,000
Debt interest rate																			4.97%			4.27%
Interest pay date																																		April 5	April 5	October 5	October 5
Description of the prepayment terms																			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			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
Prepayment terms, percent of principal before accrued and unpaid interest and "make-whole" premium																				100.00%			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.			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%			100.00%
Financial covenant description																			The Company must not permit its debt to capitalization ratio to exceed 50% at any time. The note purchase agreements generally define 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 agreements generally define the interest coverage ratio as the ratio of EBITDA for the four prior fiscal quarters to interest charges for that same period. The Company was in compliance with these covenants at June 30, 2013.			The Company must not permit its debt to capitalization ratio to exceed 50% at any time. The note purchase agreements generally define 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 agreements generally define the interest coverage ratio as the ratio of EBITDA for the four prior fiscal quarters to interest charges for that same period. The Company was in compliance with these covenants at June 30, 2013.
Debt issuance costs					1,549,000	10,800,000																																7,600,000
Interest expense on debt extinguishment	6,941,000	978,000	5,051,000	13,707,000	9,633,000
Interest expense related to amortization of debt issuance costs	$ 547,000.0		$ 617,000.0	$ 1,100,000	$ 1,200,000