Earnings per Share (Detail) - Basic Earnings Per Share - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Basic weighted-average shares (in shares)	23,738,000	23,381,000	23,606,000	23,283,000
Conversion of unsecured loan notes (in shares)	0	0	0	0
Unexercised options and unvested RSUs (in shares)	0	0	0	0
Diluted weighted-average shares (in shares)	23,738,000	23,381,000	23,606,000	23,283,000