Earnings Per Share (Restated) - Calculation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2013 Restated [Member]	Sep. 30, 2013 Restated [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income (loss) applicable to common shares	$ 8,244	$ 8,586	$ 119,907	$ 161,069
Tax-effected interest expense attributable to convertible notes	1,808		1,485	4,409
Net income assuming dilution	$ 10,052	$ 8,586	$ 121,392	$ 165,478
Weighted average common shares outstanding:
Basic shares	45,664	45,511	47,159	46,592
Effect of stock-based compensation	422	295	674	605
Effect of convertible notes	13,351		11,513	11,619
Diluted shares	59,437	45,806	59,346	58,816
Earnings (loss) per share:
Basic	$ 0.18	$ 0.19	$ 2.54	$ 3.46
Diluted	$ 0.17	$ 0.19	$ 2.05	$ 2.81