Quarterly Financial Data (Parenthetical) (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information [Line Items]
Litigation settlement expense							$ 19,000,000
Net income (loss)	66,885,000	66,358,000	63,089,000	55,863,000	58,619,000	57,660,000	45,329,000	48,334,000	252,195,000	209,942,000	149,922,000
Legal settlement
Quarterly Financial Information [Line Items]
Net income (loss)							$ (11,400,000)
Net income (loss) per share							$ (0.08)