Long-term Debt and Derivative Financial Instruments - Additional Information (Detail) (USD $)	1 Months Ended		6 Months Ended
	Apr. 30, 2013	Jul. 31, 2011	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Debt Instrument [Line Items]
Term loan				$ 100,000,000	$ 100,000,000
Debt instrument interest rate terms				Three month LIBOR plus 0.75 percent.
Debt instrument maturity date				Jun. 30, 2017
Debt instrument description of variable rate basis				0.75
Repayments of long-term debt	100,000,000
Derivative instruments, loss recognized in income	2,400,000
Line of credit facility, initiation date		Jul. 31, 2011
Debt instrument issuance date1			2013-06
Line of credit facility maximum borrowing capacity			1,000,000,000
Line of credit facility additional up-front fees			300,000
Line of credit facility frequency of commitment fee payment			Quarterly quarter
Line of credit facility, interest rate description		The interest rate for the credit facility is determined based on a formula using certain market rates, as described in the amended credit agreement.
Amended Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility maximum borrowing capacity			200,000,000
Amended Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility commitment fee amount			600,000
Amended Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Line of credit facility commitment fee amount			$ 100,000