Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 sqft	Dec. 31, 2012 sqft	Dec. 31, 2011 sqft
Commitments and Contingencies Disclosure [Line Items]
Operating Leases, Rent Expense, Net	$ 14.0	$ 14.3	$ 14.1
Size of office space leased (sqft)	15,000	15,000	15,000
Rent reimbursements related to sublease	1.1	1.2	1.1
Letter of Credit
Commitments and Contingencies Disclosure [Line Items]
Number of letters of credit issued to secure office space leases	5
Amount outstanding on letters of credit	4.2	4.2
Barrow Street III
Commitments and Contingencies Disclosure [Line Items]
Other Commitment	$ 0.3