Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Additional Information (Detail)

v2.4.0.8
Share-Based Compensation - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Share-based compensation expense $ 1.6 $ 0.6 $ 2.9 $ 1.2
Unrecognized compensation cost related to nonvested common shares $ 9.7   $ 9.7  
Weighted average period for recognition of cost     1 year 10 months 24 days