Performance Awards - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended			1 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Nov. 30, 2013 Performance Awards	Nov. 30, 2012 Performance Awards	Dec. 31, 2013 Performance Awards	Dec. 31, 2012 Performance Awards
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Total shareholder return period				3 years	3 years
Performance awards, granted				$ 1.4	$ 0.7
Performance awards, forfeitures					1.2
Performance awards, vesting period					2015-11
Performance awards, vesting period				2016
Unearned compensation expense	6.8			1.7	1.7
Compensation expense	$ 5.3	$ 4.7	$ 3.6			$ 0.2	$ 0.2