Equity Incentive Plan (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		3 Months Ended	0 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Jan. 25, 2013	Sep. 30, 2014 February 7, 2014 Grant [Member]	Jan. 25, 2013 Restricted Shares [Member]	Sep. 30, 2014 Restricted Shares [Member]	Sep. 30, 2013 Restricted Shares [Member]	Sep. 30, 2013 Restricted Shares [Member]	Sep. 30, 2014 Restricted Shares [Member]	Apr. 17, 2013 Performance Based Shares [Member]	Sep. 30, 2014 Performance Based Shares [Member]	Sep. 30, 2014 Performance Based Shares [Member] April 17, 2013 Grant [Member]	Sep. 30, 2013 Performance Based Shares [Member] April 17, 2013 Grant [Member]	Sep. 30, 2013 Performance Based Shares [Member] April 17, 2013 Grant [Member]	Sep. 30, 2014 Performance Based Shares [Member] April 17, 2013 Grant [Member]	Sep. 30, 2014 Performance Based Shares [Member] February 7, 2014 Grant [Member]	Sep. 30, 2014 Performance Based Shares [Member] February 7, 2014 Grant [Member]	Feb. 07, 2014 Performance Based Shares [Member] February 7, 2014 Grant [Member]	Sep. 30, 2014 2012 LTIP Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (in shares)																		4
Issuance of restricted shares (in shares)				1				1
Vesting period of restricted stock				3 years				3 years	3 years	3 years
Share price (in dollars per share)	$ 24.04	$ 19.00
Compensation expense					$ 1.6	$ 1.6	$ 4.3	$ 4.7			$ 0.3	$ 0.3	$ 0.6	$ 0.8	$ 0.7	$ 2.1
Unrecognized compensation expense					$ 7.6			$ 7.6			$ 1.1			$ 1.1			$ 5.1
Period of recognition	1 year 3 months 18 days
Options vested and expected to vest remaining contractual term														1 year 6 months
Other than options outstanding remaining contractual term			2 years 4 months 24 days
Target achievement percentage											60.00%			60.00%	86.00%	86.00%
Relative return target achievement											100.00%			100.00%	100.00%	100.00%