Debt - 2012 Senior Unsecured Notes - Additional Information (Detail) (2012 Senior Unsecured Notes [Member], USD $) In Millions, unless otherwise specified	0 Months Ended		12 Months Ended
	Aug. 20, 2013	Feb. 17, 2012	Dec. 31, 2013	Dec. 31, 2012
2012 Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Unsecured senior notes, value of offering	$ 150.0	$ 200.0
Unsecured senior notes, interest rate	6.375%	6.375%	6.375%	6.375%
Debt instrument, maturity date		Feb. 15, 2020	Feb. 15, 2022
Senior notes frequency of periodic payment			Semi-annually
Net proceeds, after underwriting discount	$ 150.4	$ 196.5
Senior notes, earliest redemption date			Feb. 15, 2017
Senior notes, repurchase price percentage on principal amount plus accrued and unpaid interest	101.00%	101.00%
Debt instrument redemption price	10200.00%	10200.00%
Debt instrument effective rate			5.998%