Debt (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended		3 Months Ended		0 Months Ended	3 Months Ended			3 Months Ended
	Feb. 13, 2014	Feb. 11, 2014	Mar. 31, 2014	Feb. 28, 2014	Feb. 14, 2014 Convertible Notes	Mar. 31, 2014 Convertible Notes	Feb. 28, 2014 Convertible Notes	Feb. 11, 2014 Convertible Notes	Mar. 31, 2014 Convertible Notes Conversion covenant under circumstance one D	Mar. 31, 2014 Convertible Notes Conversion covenant under circumstance two	Mar. 31, 2014 Convertible Notes Conversion covenant under circumstance two Maximum	Mar. 31, 2014 Convertible Notes Conversion covenant under circumstance three
Liability component:
Principal			$ 200,000,000
Less: debt discount, net			(37,439,000)
Net carrying amount			162,561,000			162,600,000
Equity component			38,188,000
Aggregate principal amount of notes issued					200,000,000		200,000,000
Amount pertaining to full exercise of over-allotment of debt by underwriters					25,000,000
Proceeds from issuance of convertible debt			200,000,000		193,300,000
Fees and expenses					6,700,000
Proceeds used to pay the cost of the bond hedges (after such cost was partially offset by proceeds from the sale of warrants)			14,100,000		14,100,000
Interest rate (as a percent)			2.50%			2.50%
Initial conversion rate of common stock per $1000 of principal amount of Notes (in shares)						36.9079
Principal amount used for debt instrument conversion ratio						1,000				1,000		1,000
Initial conversion price of convertible notes into common stock (in dollars per share)						$ 27.09
Conversion premium (as a percent)						35.00%
Sale price of common stock (in dollars per share)								$ 20.07
Number of days during 30 consecutive trading days in which the closing price of the entity's common stock must exceed or equal the conversion price for the notes to be convertible									20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed or equal the conversion price for at least 20 days in order for the notes to be convertible									30 days
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed or be equal in order for the notes to be convertible									130.00%
Number of consecutive business days after any five consecutive trading day period during the note measurement period										5 days
Number of consecutive trading days before five consecutive business days during the note measurement period										5 days
Percentage of product of the last reported sale price of the entity's common stock and the conversion rate of convertible debt instruments											98.00%
Repurchase price as a percentage of principal amount of notes plus accrued and unpaid interest						100.00%
Minimum percentage of principal amount held by holders to declare notes due and payable						25.00%
Percentage of principal amount due and payable in an event of default						100.00%
Percentage of principal amount due and payable in the event of default, arising out of certain events of bankruptcy, insolvency or reorganization						100.00%
Maximum period to comply any remedy for specified event of default relating to certain failures						270 days
Debt issuance costs allocated to equity component			1,300,000		1,300,000
Debt issuance costs allocated to the liability component					5,400,000
Expected life of the debt						5 years
Effective interest rate on liability component (as a percent)						7.23%
Total interest expense recognized
Contractual interest expense						625,000
Amortization of debt issuance costs						102,000
Amortization of debt discount						749,000
Total interest expense			1,476,000			1,476,000
Convertible Bond Hedge
Common stock covered under convertible bond hedge (in shares)	7.4	7.4
Exercise price (in dollars per unit)	$ 27.09	$ 27.09
Purchase of convertible bond hedge			39,760,000
Warrant Transactions
Number of shares of common stock called by warrants				7.4
Exercise price (in dollars per share)				$ 34.12
Exercise price above last reported sale price of common stock (as a percent)				70.00%
Amount received on warrants sold			$ 25,620,000