Revolving Line of Credit - Additional Information (Detail) (USD $)	6 Months Ended			1 Months Ended		6 Months Ended
	Jun. 30, 2013 Basis	Jun. 30, 2012	Sep. 05, 2012	Jul. 30, 2013 Subsequent Event [Member]	Jul. 16, 2013 Subsequent Event [Member]	Jun. 30, 2013 Leverage ratio less than 0.5 to 1.0 [Member] LIBOR rate loans [Member]	Jun. 30, 2013 Leverage ratio less than 0.5 to 1.0 [Member] Base rate loans [Member]	Jun. 30, 2013 Leverage ratio greater than 0.5 to 1.0 but less than 1.0 to 1.0 [Member] LIBOR rate loans [Member]	Jun. 30, 2013 Leverage ratio greater than 0.5 to 1.0 but less than 1.0 to 1.0 [Member] Base rate loans [Member]	Jun. 30, 2013 Leverage ratio greater than 1.0 to 1.0 [Member] LIBOR rate loans [Member]	Jun. 30, 2013 Leverage ratio greater than 1.0 to 1.0 [Member] Base rate loans [Member]	Jun. 30, 2013 Maximum [Member] Basis	Jun. 30, 2013 Minimum [Member] Basis
Line of Credit Facility [Line Items]
Credit agreement revolving line of credit facility	$ 75,000,000
Line of credit facility maximum borrowing capacity	125,000,000				50,000,000
Credit Facility expiry date	Sep. 05, 2014
Line of credit facility interest rate	4.25%
Consolidated leverage ratio						1.75%	0.75%	2.00%	1.00%	2.25%	1.00%
LIBOR floor base rate	1.00%
Interest expense	572,000
Loan costs and fees to be amortized using the effective interest method over 24 months	976,000
Amortization expense included in interest expense in the consolidated statement of income	244,000	0
Percentage of maximum amount of unused line fee	0.625%
Percentage of minimum amount of unused line fee	0.375%
Fees relating to unused capacity	118,000
Applicable margin for credit facility based on consolidated interest coverage ratio, Maximum	3.00
Applicable margin for credit facility based on consolidated interest coverage ratio, Minimum	1.00
Consolidated funded indebtedness												2.00	1.00
Revolving credit facility, amount			50,000,000
Letters of credit outstanding revolving credit facility	50,000,000
Credit facility, available to borrow	25,000,000
Repayment of revolving credit facility				$ 25,000,000