Financial Instruments (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended								1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Private Placement, Notes [Member]	Dec. 31, 2012 Credit Agreement [Member]	Dec. 31, 2012 Credit Agreement [Member] Interest Rate Swap [Member]	Oct. 16, 2012 Credit Agreement [Member] Interest Rate Swap [Member]	Oct. 12, 2012 Credit Agreement [Member] Interest Rate Swap [Member]	Jan. 25, 2013 Convertible Notes [Member]	Dec. 31, 2012 Convertible Notes [Member]	Dec. 31, 2012 Senior Notes [Member]	Dec. 31, 2012 Warrant [Member]
Debt Instrument [Line Items]
Principal payments due in 2013	$ 83,300,000
Principal payments due in 2014	3,800,000
Principal payments due in 2015	182,000,000
Principal payments due in 2016	100,000
Principal payments due in 2017	50,000,000
Principal payments due 2018 and thereafter	100,000
Interest paid	18,400,000	20,200,000	17,400,000
Debt issued				150,000,000						28,437,000
Interest rate				6.84%						2.25%
Maturity date				Oct. 25, 2017
Year of maturity					2015					2026
Payment required on October 25, 2013				50,000,000
Payment required on October 25, 2015				50,000,000
Fair value of long-term debt				171,900,000						28,400,000
Amount of credit facility					390,000,000
Amount of credit facility outstanding					132,000,000
Additional amount that can be borrowed on facility					258,000,000
Notional amount						105,000,000
Fixed interest rate in swap						2.04%		0.34%
LIBOR spread							2.25%
Effective annual rate							4.29%
Maximum leverage ratio allowed	3.5
Minimum interest coverage ratio required	3
Leverage ratio	1.06
Interest coverage ratio	13.31
Percentage of principal redeemed									100.00%
Date when holders may convert										Feb. 15, 2013
Shares per $1,000 of principal										23.2078
Minimum per share distribution value allowing conversion										15.00%
Percent of product which allows conversion										103.00%
Conversion price										$ 43.09
Note hedge and warrant, net cost										14,700,000
Number of warrants sold										4.1
Strike price of warrants										52.25
Carrying amount of equity component										$ 25,500,000
Incremental net shares will be included in future diluted earnings per share, maximum average common stock price											$ 43.09	$ 49.2