Long-Term Debt - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	May 02, 2013	Mar. 30, 2013
Unsecured private placement notes
Line of Credit Facility [Line Items]
Interest rate spread on notes (in percent)		0.60%
Long-term debt, notes		$ 75,000,000
Long-term debt maturities		Jun. 30, 2015
Outstanding balance, notes		75,000,000
Interest rate on notes (in percent)		0.91%
Debt Instrument, description of variable rate basis		The notes bear interest at 0.60% over LIBOR
Debt instrument, frequency of periodic payment		The notes do not require principal payments until maturity
Unsecured revolving credit facility
Line of Credit Facility [Line Items]
Revolving credit facility		250,000,000
Debt facility expiration date		Mar. 07, 2017
Borrowings outstanding under the revolving credit facility		88,500,000
Letters of credit sub-limit		50,000,000
Outstanding letters of credit		600,000
Interest rate (in percent)		1.70%
Fee payment on unused credit balances, percentage		0.25%
Debt amendment date	Apr. 12, 2013
Effective date of debt amendment, latest	Jun. 30, 2015
Line of credit facility, interest rate description		Borrowings in U.S. dollars under this credit facility, at our election, bear interest at (a) adjusted LIBOR for specified interest periods plus a margin, which can range from 1.00% to 2.00%, determined with reference to our consolidated leverage ratio or (b) a floating rate equal to the greatest of (i) JPMorgan's prime rate, (ii) the federal funds rate plus 0.50% and (iii) the adjusted LIBOR for a one month interest period plus 1.00%, plus, in each case, a margin determined with reference to our consolidated leverage ratio. Base rate loans will, at our election, bear interest at (i) the rate described in clause (b) above or (ii) a rate to be agreed upon by us and JPMorgan. Borrowings in Canadian dollars under the credit facility will bear interest at (a) the Canadian deposit offered rate plus 0.10% for specified interest periods plus a margin determined with reference to our consolidated leverage ratio or (b) a floating rate equal to the greater of (i) the Canadian prime rate and (ii) the Canadian deposit offered rate for a one month interest period plus 1.00%, plus, in each case, a margin determined with reference to our consolidated leverage ratio.
Unsecured revolving credit facility | Condition A in US Dollars
Line of Credit Facility [Line Items]
Line of credit facility, interest rate description		The adjusted LIBOR for specified interest periods plus a margin, which can range from 1.00% to 2.00%, determined with reference to our consolidated leverage ratio
Unsecured revolving credit facility | Condition B-ii in US Dollars
Line of Credit Facility [Line Items]
Interest rate spread on notes (in percent)		0.50%
Line of credit facility, interest rate description		Federal funds rate plus 0.50%
Unsecured revolving credit facility | Condition B-iii in US Dollars
Line of Credit Facility [Line Items]
Interest rate spread on notes (in percent)		1.00%
Line of credit facility, interest rate description		The adjusted LIBOR for a one month interest period plus 1.00%, plus, in each case, a margin determined with reference to our consolidated leverage ratio.
Unsecured revolving credit facility | Condition A in Canadian Dollars
Line of Credit Facility [Line Items]
Interest rate spread on notes (in percent)		0.10%
Line of credit facility, interest rate description		The Canadian deposit offered rate plus 0.10% for specified interest periods plus a margin determined with reference to our consolidated leverage ratio.
Unsecured revolving credit facility | Condition B-ii in Canadian Dollars
Line of Credit Facility [Line Items]
Interest rate spread on notes (in percent)		1.00%
Line of credit facility, interest rate description		The Canadian deposit offered rate for a one month interest period plus 1.00%, plus, in each case, a margin determined with reference to our consolidated leverage ratio.
Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility		50,000,000
Debt facility expiration date		Sep. 27, 2013
Interest rate spread on notes (in percent)		0.76%
Borrowings outstanding under the revolving credit facility		23,800,000
Outstanding letters of credit		$ 26,200,000
Interest rate (in percent)		0.96%
Line of credit facility, interest rate description		We pay interest at a rate per annum equal to a margin of 0.76%, plus LIBOR.
Minimum | Unsecured revolving credit facility | Condition A in US Dollars
Line of Credit Facility [Line Items]
Interest rate spread on notes (in percent)		1.00%
Maximum | Unsecured revolving credit facility | Condition A in US Dollars
Line of Credit Facility [Line Items]
Interest rate spread on notes (in percent)		2.00%