Earnings per Share (Detail) - Basic Earnings Per Share - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Basic weighted-average shares (in shares)	24,133,000	23,446,000	23,784,000	23,337,000
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)	24,133,000	23,446,000	23,784,000	23,337,000