Share-based Compensation Expense - Share-based Compensation Expense by Types of Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 5,068	$ 5,888	$ 11,225	$ 12,997
Performance rights
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	7	3,262	575	4,103
Restricted stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	454	1,796	3,645	6,754
Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 4,607	$ 830	$ 7,005	$ 2,140