Share-Based Compensation Expense by Types of Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 5,888	$ 3,837	$ 12,997	$ 17,022
Performance Rights
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	3,262	427	4,103	1,121
Restricted stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	1,796	2,864	6,754	12,512
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 830	$ 546	$ 2,140	$ 3,389