Share-Based Compensation - Additional Information (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted	0	15,577	107,296	58,962
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted	45,280	68	45,280	221,365
Performance-Based Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted	0	0	634,778	0