Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013 sqft	Dec. 31, 2012 sqft
Commitments and Contingencies Disclosure [Line Items]
Operating Leases, Rent Expense, Net	$ 14,600,000	$ 14,000,000	$ 14,300,000
Size of office space leased (sqft)		15,000	15,000
Rent reimbursements related to sublease		1,100,000	1,200,000
Letter of Credit
Commitments and Contingencies Disclosure [Line Items]
Number of letters of credit issued to secure office space leases	6
Amount outstanding on letters of credit	5,700,000	4,200,000
Barrow Street III
Commitments and Contingencies Disclosure [Line Items]
Other Commitment	$ 300,000