Taxation - Reconciliation of Earnings before Income Taxes Computed by Applying Effective Rate (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income Taxes [Line Items]
Earnings before income tax	$ 70,192	$ 26,484	$ 142,096	$ 48,164
Expected tax rate	0.00%	0.00%	0.00%	0.00%
Foreign taxes at local expected rates	26.10%	33.90%	24.40%	38.20%
Change in uncertain tax positions	0.10%	(0.20%)	0.10%	0.30%
Change in valuation allowance	(5.40%)	(18.10%)	(3.30%)	(24.70%)
Impact of Australian tax consolidation	0.00%	0.00%	0.00%	(1.90%)
Other	0.10%	1.10%	0.20%	0.70%
Effective tax rate	20.90%	16.70%	21.40%	12.60%