Convertible Senior Notes Due 2017 - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 21, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 21, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Long Term Debt [Line Items]
Debt instrument, offering date					Mar. 19, 2012
Convertible Notes, maturity date					Apr. 01, 2017
Convertible Notes, payment terms					The Convertible Notes bear interest at a rate of 2.625% per annum, payable semi-annually in arrears on April 1 and October 1 of each year, beginning on October 1, 2012.
Convertible Notes, aggregate principal amount		$ 258,800,000			$ 258,800,000
Maximum percentage of conversion price upon redemption of Convertible Notes					130.00%
Percentage of redemption price to principal amount of note					100.00%
Convertible Notes, conversion term description					(1) during any calendar quarter commencing after the calendar quarter ending on June 30, 2012, if the closing sale price of the Company’s common stock, for at least 20 trading days (whether or not consecutive) in the period of 30 consecutive trading days ending on the last trading day of the calendar quarter immediately preceding the calendar quarter in which the conversion occurs, is more than 130% of the conversion price of the Convertible Notes in effect on each applicable trading day; (2) during the five consecutive trading-day period following any five consecutive trading-day period in which the trading price for the Convertible Notes for each such trading day was less than 98% of the closing sale price of the Company’s common stock on such date multiplied by the then-current conversion rate; (3) upon the occurrence of specified corporate events; or (4) if the Company calls any Convertible Notes for redemption, at any time until the close of business on the second business day preceding the redemption date. On or after January 1, 2017 until the close of business on the second business day immediately preceding the stated maturity date, holders may surrender their Convertible Notes for conversion at any time, regardless of the foregoing circumstances. At September 30, 2013, the Convertible Notes were not convertible.
Debt instrument convertible conversion ratio presplit				9.7586
Debt instrument convertible increment of principal amount of conversion	1,000				1,000
Debt instrument convertible conversion price1 presplit	$ 102.47			$ 102.47
Conversion rate of common stock, shares per principal amount	19.5172
Conversion price, per share of common stock	$ 51.24			$ 51.24
Amortization of debt discount		3,200,000	2,900,000		9,200,000	6,000,000
Convertible notes, net of unamortized discount		205,173,000			205,173,000		196,007,000
Recognized debt discount		53,577,000			53,577,000		62,743,000
Issuance costs					8,400,000
Convertible Notes, issuance costs allocated to equity component					2,300,000
Convertible Notes, issuance costs allocated to debt component					6,100,000
Interest expense on Convertible Notes		5,165,000	4,840,000		15,035,000	10,113,000
2.625% convertible senior notes due 2017 [Member]
Long Term Debt [Line Items]
Debt instrument, interest rate		2.625%	2.625%		2.625%	2.625%
Debt instrument, effective percentage rate		10.71%	10.71%		10.71%	10.71%
Interest expense on Convertible Notes		5,200,000	4,800,000		15,000,000	10,100,000
Cash interest expenses		1,700,000	1,700,000		5,100,000	3,600,000
Non-cash interest expense		3,500,000	3,100,000		9,900,000	6,500,000
Equity component [Member]
Long Term Debt [Line Items]
Convertible Notes, equity component		71,700,000			71,700,000
Debt component [Member]
Long Term Debt [Line Items]
Debt instrument convertible debt equity component					$ 187,100,000
Common stock [Member]
Long Term Debt [Line Items]
Forward stock split of common stock					2