Financing Arrangements (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 01, 2011
Convertible Notes [Abstract]
Carrying amount of the liability component	$ 108,750,000	$ 104,637,000
Deferred financing cost amortization	842,000	782,000	1,948,000
Convertible Senior Notes [Member]
Convertible Notes [Abstract]
Aggregate principal amount in debt offering				120,000,000
Interest rate (in hundredths)	3.50%
Aggregate principal amount of debt issued upon exercise by the buyers of their full over-allotment option				20,000,000
Net proceeds from the issuance of debt			115,300,000
Maturity date	Jun. 01, 2016
Debt conversion price (in dollars per share)	$ 8.76
Debt conversion ratio	114.1553
Debt conversion ratio numerator	1,000
Notes Trading Price to Face Value (in hundredths)	284.00%
Fair market value of Convertible Notes	341,300,000
Closing price of common stock (in dollars per share)	$ 24.62
Pro forma debt instrument conversion amount	337,300,000
Terms of conversion feature	The Notes may be converted at any time prior to the close of business on the business day immediately preceding December 1, 2015 only under the following circumstances:  (1) during any calendar quarter commencing after September 30, 2011, if the closing sale price of the Company’s common stock, for at least 20 trading days (whether or not consecutive) during 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 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 Notes per $1,000 principal amount of 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; or (3) upon the occurrence of specified corporate events.
Required price of common stock for note convertibility (in dollars per share)	$ 11.39
Carrying amount of equity component	20,470,000	20,470,000
Carrying amount of the liability component	108,750,000	104,637,000
Unamortized discount of the liability component	11,250,000	15,363,000
Unamortized debt financing costs	2,034,000	2,778,000
Debt issuance costs	4,700,000
Debt issuance cost allocated to the liability component of debt	3,900,000
Debt issuance cost allocated to the equity component of debt	800,000
Coupon rate (in hundredths)	3.50%	3.50%	3.50%
Interest expense at 3.50% coupon rate	4,200,000	4,200,000	2,450,000
Debt discount amortization	4,113,000	3,828,000	2,109,000
Deferred financing cost amortization	744,000	692,000	382,000
Total expenses	9,057,000	8,720,000	4,941,000
Deferred tax liability				8,600,000
Debt discount				$ 21,300,000