Debt - Additional Information (Detail) (USD $)	1 Months Ended	6 Months Ended		12 Months Ended					6 Months Ended		1 Months Ended			1 Months Ended
	Mar. 11, 2013	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2011	Dec. 31, 2012	Feb. 10, 2012	Jun. 30, 2013 Parent Company and Domestic Subsidiaries	Jun. 30, 2013 Foreign Subsidiaries	Jun. 30, 2013 Maximum	Jun. 30, 2013 Minimum	Feb. 10, 2012 Revolving Credit Facility	Nov. 10, 2011 Revolving Credit Facility	Jun. 30, 2013 Revolving Credit Facility Maximum	Feb. 10, 2012 Term Credit Facility	Nov. 10, 2011 Term Credit Facility
Debt Instrument [Line Items]
Credit facilities, maximum borrowing capacity												$ 250,000,000			$ 500,000,000
Credit facilities, maturity												5 years			5 years
Unused borrowings													62,000,000
Note payable under credit facility		188,000,000			188,000,000	370,000,000						75,000,000
Additional borrowing under credit facility	300,000,000		95,000,000								95,000,000			200,000,000
Deferred debt issuance cost						12,800,000
Debt issuance cost, paid		9,536,000	553,000	11,800,000
Debt issuance costs		9,500,000
Credit facility, interest rate description		The applicable margin for borrowings under the Revolving Credit Facility is, based on the calculation of the applicable consolidated total leverage ratio, between 0.50% to 1.50% with respect to base rate borrowings and between 1.50% and 2.50% with respect to LIBOR based borrowings. Interest is due and payable monthly. The interest rate in effect at June 30, 2013 was 2.45%.
Credit facility, interest rate margin above federal fund rate		0.50%
Credit facility, interest rate margin above one-month LIBOR rate		1.00%
Credit facility, interest rate margin above base rate									1.50%	0.50%
Credit facility, interest rate margin above LIBOR rate									2.50%	1.50%
Credit facility, borrowing rate		2.45%
Repayment of term portion of credit agreement		$ 13,125,000	$ 6,250,000
Credit Facility maturity date		Nov. 10, 2016
Percentage of capital stock pledged as collateral							100.00%	65.00%