Convertible Senior Notes Due 2017 - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Sep. 21, 2012	Dec. 31, 2014 D	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
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
Debt instrument, interest rate		2.625%
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.
Number of trading days		20
Consecutive trading days		30 days
Conversion rate of common stock, shares per principal amount	19.5172	19.5172
Debt instrument convertible increment of principal amount of conversion	1,000	1,000
Conversion price, per share of common stock	$ 51.24	$ 51.24
Issuance costs		8,400,000
Convertible Notes, issuance costs allocated to debt component		6,100,000
Additional Paid-In Capital [Member]
Debt Instrument [Line Items]
Convertible Notes, issuance costs allocated to equity component		2,300,000
Equity component [Member]
Debt Instrument [Line Items]
Convertible Notes, equity component		71,700,000
Debt component [Member]
Debt Instrument [Line Items]
Debt instrument convertible debt equity component		$ 187,100,000
2.625% convertible senior notes due 2017 [Member]
Debt Instrument [Line Items]
Debt instrument, effective percentage rate		10.71%	10.71%	10.71%