Reconciliation of Weighted Average Shares Used in Computation of Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share Disclosure [Line Items]
Net income (loss) available to common stockholders	$ 36,597	$ 30,443	$ (37,838)	$ 14,657
Net income (loss) available to common stockholders plus assumed exercises and conversion	37,951	31,732	(37,838)	18,524
Earnings (loss) per share - basic
Net income (loss) available to common stockholders	21,920	22,110	21,922	24,656
Effect of dilutive securities:
Convertible senior notes	12,294	6,707		6,520
Options and warrants		5		6
Unvested restricted stock grants	69	111		92
Earnings (loss) per share - diluted
Net income (loss) available to common stockholders plus assumed exercises and conversion	34,283	28,933	21,922	31,274
Earnings (loss) per share - basic
Net income (loss) available to common stockholders	$ 1.67	$ 1.38	$ (1.73)	$ 0.59
Earnings (loss) per share - diluted
Net income (loss) available to common stockholders plus assumed exercises and conversion	$ 1.11	$ 1.10	$ (1.73)	$ 0.59
4.50% Convertible senior notes
Earnings Per Share Disclosure [Line Items]
Effect of dilutive securities	$ 1,354	$ 1,289		$ 3,867