Convertible Notes, Long-Term Debt and Credit Facility - Convertible Notes (Details) (USD $)	0 Months Ended	3 Months Ended		6 Months Ended			0 Months Ended			1 Months Ended	6 Months Ended			0 Months Ended	6 Months Ended
	Feb. 14, 2008	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2010	Dec. 31, 2012 2008 Notes [Member]	Jun. 25, 2012 2008 Notes [Member]	Feb. 14, 2008 2008 Notes [Member]	May 31, 2011 2008 Notes [Member]	Jun. 30, 2013 2008 Notes [Member]	Feb. 15, 2013 2008 Notes [Member]	Mar. 31, 2010 2008 Notes [Member]	Jan. 05, 2012 2010 Notes [Member]	Jun. 30, 2013 2010 Notes [Member]	Mar. 31, 2010 2010 Notes [Member]	Mar. 31, 2010 Exchange Agreement [Member]
Debt Instrument [Line Items]
Notes repurchased							$ 50,300,000	$ 15,000,000				$ 5,200,000		$ 36,000,000
Principal amount									115,000,000
Convertible notes, interest rate									5.25%
Convertible notes maturity date									Feb. 15, 2028						Feb. 15, 2028
Nonconvertible debt borrowing interest rate											11.50%
Expected term for accretion of associated debt discount (in years)											5 years
Contractual call/put options, exercisable date											Feb. 15, 2013
Effective tax rate	38.00%	35.00%	35.00%	35.00%	35.00%
Discount on notes									27,800,000
Deferred tax liability on notes		9,030,000		9,030,000					10,600,000
Value of common stock shares																	2,000,000
Convertible notes for each $1,000 principal amount, amount of notes exchanged													40,000,000
Convertible notes for each $1,000 principal amount, amount of aggregate consideration																36,000,000
Assumed rate of accretion on notes						9.90%
Cash redeemed, percent of outstanding principal amount											100.00%
Convertible notes for each $1,000 principal amount, number of shares				43.9560
Convertible notes for each $1000 principal amount, principal amount of notes converted		1,000		1,000
Convertible notes for each $1,000 principal amount, conversion price per share		$ 22.75		$ 22.75
Amount of notes exchanged										4,500,000
Percentage of original principal amount of notes plus accrued and unpaid interest equalized repurchase								102.00%						104.95%
Convertible notes for each $1,000 principal amount, number of shares										559,007
Loss on the extinguishment of debt							900,000	1,000,000		1,100,000				5,400,000
Cash premium loss recognized on conversion of debt				$ (55,000)	$ (2,031,000)		$ 300,000	$ 300,000						$ 1,800,000