Share-based Compensation - Additional Information (Detail) - USD ($)					3 Months Ended		9 Months Ended
	Sep. 30, 2015	Aug. 05, 2015	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense recognized					$ 1,900,000	$ 1,700,000	$ 5,500,000	$ 4,100,000
Shares issued under stock purchase plan					43,326	69,572	271,166	501,862
Performance Based [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Non-vested shares		41,910	68,750	99,600
Restricted Stock [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense recognized	$ 0