Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net income / (loss)	$ (79,456)	$ 60,184
Weighted average shares of common stock outstanding (used to calculate basic EPS)	81,538	72,885
Net effect of dilutive employee stock options based on the treasury stock method	465	217
Weighted average shares of common stock outstanding (used to calculate diluted EPS)	82,003	73,102
Net income / (loss) per common share - basic	$ (0.97)	$ 0.83
Net income / (loss) per common share - diluted	$ (0.97)	$ 0.82