Special Charges - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012 Location Employee
Special Charges [Line Items]
Special charges	$ 400,000	$ 26,782,000	$ 427,000	$ 26,782,000	$ 29,600,000
Non cash special charges					5,000,000
Number of employees terminated					116
Number of office locations					9
Cash outflow associated with special charges, amount paid			24,700,000
Cash outflow associated with special charges, amount paid			13,100,000
Cash outflow associated with special charges, amount expected to be paid in 2013			3,200,000
Cash outflow associated with special charges, amount expected to be paid in 2014			2,700,000
Cash outflow associated with special charges, amount expected to be paid in 2015			1,200,000
Cash outflow associated with special charges, amount expected to be paid in 2016			800,000
Cash outflow associated with special charges, amount expected to be paid from 2017 to 2025			$ 3,700,000