Quarterly Financial Data (Parenthetical) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information [Line Items]
Litigation settlement expense			$ 19,000
Net income (loss)	58,619	57,660	45,329	[1]	48,334	42,624	44,168	36,425	26,705	209,942	149,922	66,069
Legal Settlement
Quarterly Financial Information [Line Items]
Net income (loss)			$ (11,400)
Net income (loss) per share			$ (0.08)

[1] The decrease in second quarter 2012 income before income taxes, net income, and net income per share was primarily due to a charge related to a litigation settlement disclosed in the Company's July 5, 2012, Form 8-K. The settlement resulted in a non-recurring $19.0 million pre-tax charge to selling, general and administrative expenses and reduced second quarter net income and net income per share by $11.4 million and $0.08 per share, respectively.