Represents the percentage of the closing sales price of the entity's common stock for at least 20 days within 30 consecutive trading days that the closing sales price of the entity's common stock must exceed the applicable conversion price in order for the debt instruments to be redeemable at the reporting entity's option.

No definition available.

Convertible Notes (Narrative) (Details)			12 Months Ended
Convertible Notes (Narrative) (Details)	Aug. 16, 2013 USD ($) $ / shares	Jun. 29, 2009 USD ($) shares $ / shares	Dec. 31, 2016 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($)	Jul. 10, 2009 USD ($)	Jun. 28, 2009 USD ($)
Events of default
Additional paid in capital			$ 1,181,230,000			$ 1,130,368,000
Convertible notes
Events of default
Additional paid in capital			93,400,000			93,400,000
Convertible notes \| 1.125% Convertible Senior Notes due 2018
Debt Instrument [Line Items]
Face Value	$ 138,000,000		$ 138,000,000			$ 138,000,000
Liability Component, Principal amount	107,700,000
Equity Component, Principal amount	$ 30,300,000
Debt discount amortization period	5 years		20 months
Stated Interest rate (as a percent)	1.125%
Debt Issuance Cost, Convertible, Liability Component	$ 2,800,000
Debt Issuance Cost, Convertible, Equity Component	$ 800,000
Debt Instrument, Term	5 years
Debt Issuance Costs, Gross	$ 3,600,000
Conversion rate, number of shares to be issued per $1000 of principal (in shares)	82.8329
Principal amount of notes used as the denominator to determine number of shares converted into notes	$ 1,000
Initial conversion price of notes (in dollars per share) \| $ / shares	$ 12.07
Number of trading days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable, minimum	20 days
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be redeemable	30 days
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be convertible	130.00%
Number of business days immediately after any ten consecutive trading day period during the note measurement period	5 days
Number of consecutive trading days before the five business days during the debt instrument measurement period	5 days
Denomination of the principal amount of notes used to calculate the percent of trading price during the debt instrument measurement period	$ 1,000
Maximum conversion price as a percentage of closing stock price	98.00%
Percentage of face amount of debt instrument redeemable at the company's option	100.00%
Events of default
Period of default in payment of interest (in days)	30 days
Period of default to comply with other agreements (in days)	60 days
Minimum percentage of aggregate outstanding principal required for default event with other agreements	25.00%
Minimum principal amount of debt nonpayment required for debt default to occur	$ 40,000,000
Period of nonpayment of principal amount required for debt default to occur (in days)	30 days
Minimum percentage of aggregate outstanding principal required for nonpayment of debt default to occur	25.00%
Minimum percentage of aggregate outstanding principal required for immediate payment declaration to occur	25.00%
Convertible notes \| 5% Convertible Senior Notes due 2014
Debt Instrument [Line Items]
Face Value		$ 150,000,000					$ 22,500,000
Liability Component, Principal amount		92,400,000					14,300,000
Equity Component, Principal amount		$ 57,600,000					$ 8,200,000
Debt discount amortization period		5 years
Stated Interest rate (as a percent)		5.00%
Debt Issuance Cost, Convertible, Liability Component		$ 3,200,000
Debt Issuance Cost, Convertible, Equity Component		$ 1,900,000
Debt Instrument, Term		5 years
Periodic interest payment				$ 4,300,000	$ 8,600,000
Debt Issuance Costs, Gross								$ 5,100,000
Conversion rate, number of shares to be issued per $1000 of principal (in shares)		51.8
Principal amount of notes used as the denominator to determine number of shares converted into notes		$ 1,000
Initial conversion price of notes (in dollars per share) \| $ / shares		$ 19.31
Number of trading days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable, minimum		20 days
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be redeemable		30 days
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be convertible		130.00%
Number of business days immediately after any ten consecutive trading day period during the note measurement period		5 days
Number of consecutive trading days before the five business days during the debt instrument measurement period		10 days
Denomination of the principal amount of notes used to calculate the percent of trading price during the debt instrument measurement period		$ 1,000
Maximum conversion price as a percentage of closing stock price		98.00%
Number of trading days conversion reference period		20 days
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be redeemable at the company's option		30 days
Percentage of face amount of debt instrument redeemable at the company's option		100.00%
Number of trading days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable at the company's option, minimum		20 days
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be redeemable at the company's option		130.00%
Percentage of face amount which may be redeemed by the debt holder for cash upon occurrence of a fundamental change		100.00%
Maximum increase in conversion rate per $1000 principal amount upon occurrence of fundamental change \| shares		15.5401
Events of default
Period of default in payment of interest (in days)		30 days
Period of default to comply with other agreements (in days)		60 days
Minimum percentage of aggregate outstanding principal required for default event with other agreements		25.00%
Minimum principal amount of debt nonpayment required for debt default to occur		$ 30,000,000
Period of nonpayment of principal amount required for debt default to occur (in days)		10 days
Minimum percentage of aggregate outstanding principal required for nonpayment of debt default to occur		25.00%
Minimum percentage of aggregate outstanding principal required for immediate payment declaration to occur		25.00%
Convertible Senior Notes [Member] \| 1.125% Convertible Senior Notes due 2018
Debt Instrument [Line Items]
Stated Interest rate (as a percent)	1.125%		1.125%	1.125%		1.125%
Convertible Senior Notes [Member] \| 5% Convertible Senior Notes due 2014
Debt Instrument [Line Items]
Stated Interest rate (as a percent)				5.00%
Events of default
Repayments of Debt				$ 172,500,000