Share-Based Compensation - RSAs and PSAs Granted and Vesting Schedule of Awards (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	292,193
At Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	9,194
After Three Years Of Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	282,999
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	185,782	423,644	167,515
Restricted Stock Awards | At Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	9,194
Restricted Stock Awards | After Three Years Of Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	176,588
Performance Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	106,411	233,111	187,794
Performance Share Awards | At Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	0
Performance Share Awards | After Three Years Of Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted	106,411