Share-based Compensation - Additional Information (Detail) - USD ($)			3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense recognized			$ 1,800,000	$ 1,186,000	$ 3,576,000	$ 2,373,000
Shares issued under stock purchase plan			81,974	168,715	227,840	432,290
Performance Based [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Non-vested shares	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