Debt Convertible Debt (Details) (USD $)	1 Months Ended	12 Months Ended
	Nov. 30, 2010	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Nov. 20, 2012
Debt Instrument
Amortization of Financing Costs		$ 1,100,000		$ 1,100,000
Amortization of Debt Discount (Premium)		1,931,000		1,833,000		1,738,000
Share Price		$ 40,090
Convertible notes [Member]
Debt Instrument
Amortization of Financing Costs		500,000		500,000		500,000
Revolving Credit Facility [Member]
Debt Instrument
Amortization of Financing Costs						1,300,000
Convertible notes [Member]
Debt Instrument
Debt Instrument, Face Amount	115,000,000	115,000,000		115,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.25%
Proceeds from Convertible Debt	111,000,000
Use of Debt Proceeds to Repay Borrowings on Revoloving Credit Agreement	62,200,000
Use of Debt Proceeds to Contribute to Qualified Pension Plan	25,000,000
Use of Debt Proceeds for the Purchase of Call Options Related to Convertible Note Offering	13,200,000
Convertible Debt, Features, Closing Sale Price of Common Stock Exceeding Current Converstion Price		130.00%
Conversion Feature, Percentage of Average of Closing Sale Price of Common Stock		98.00%
Purchase of call options related to convertible notes	13,200,000
Conversation Price Trading Days Prerequisite		20 days
Consecutive Trading Days Ending On The Last Trading Day Of The Previous Fiscal Quarter		30 days
Allows for acquistion of shares related to covertible debt	3,400,000
Proceeds from Issuance of Warrants	1,900,000
Conversion rate	29.4499	29.6876	[1]	29.6292	[1]
Conversion Price		$ 33.68	[2]	$ 33.75	[2]		$ 33.96
Contingent conversion price		$ 43.79	[3]	$ 43.88	[3]
Aggregate shares to be issued upon conversion, convertible		3,414,074	[4]	3,407,357	[4]
Warrant price		$ 44.05		$ 44.14
Convertible debt, carrying value of liability	101,700,000	109,024,000		107,093,000
Debt Instrument, Convertible, Carrying Amount of Equity Component	13,300,000	13,329,000		13,329,000
Present Value Discount Rate	5.25%
Deferred Finance Costs, Gross	3,600,000					3,100,000
Amortization of Financing Costs	500,000
Debt Instrument, Unamortized Discount		5,976,000		7,907,000
Contractual Coupon Rate of Interest Associated Interest Expense		3,738,000		3,738,000		3,738,000
Amortization of Debt Discount (Premium)		1,931,000		1,833,000		1,738,000
Debt Instrument, Convertible, Interest Expense		5,669,000		5,571,000		5,476,000
Debt Instrument, Convertible, If-converted Value in Excess of Principal		21,700,000
Convertible Notes Payable, Noncurrent		109,000,000
JPMorgan Chase Bank NA as Administrative Agent Bank of America NA and RBS Citizens NA as Co-Syndication Agents [Member]
Debt Instrument
Deferred Finance Costs, Gross							$ 2,400,000

[1] Represents the number of shares of Common Stock hypothetically issuable per $1,000 principal amount of Notes, subject to adjustments per the Convertible Note Indenture dated November 19, 2010. At the date the Company issued the Convertible Notes, the conversion rate initially equaled 29.4499 shares of common stock per $1,000 principal amount of notes (which is equivalent to an initial conversion price of approximately $33.96 per share of common stock). The conversion rate is subject to adjustment upon the occurrence of certain specified events, such as an increase in the dividend paid to shareholders.

[2] Represents $1,000 divided by the conversion rate as of such date. The conversion price reflects the strike price of the embedded option within the Convertible Note. Were the Company's share price to exceed the conversion price at conversion the noteholders would be entitled to receive additional consideration either in cash, shares or a combination, the form of which is at the sole discretion of the Company.

[3] Prior to May 15, 2017, the notes are convertible only in the following circumstances: (1) during any fiscal quarter commencing after April 1, 2011, and only during any such fiscal quarter, if the last reported sale price of our common stock was greater than or equal to 130% of the applicable conversion price for at least 20 trading days (whether or not consecutive) during the 30 consecutive trading days ending on the last trading day of the previous fiscal quarter, (2) upon the occurrence of specified corporate transactions, or (3) during the five consecutive business-day period following any five consecutive trading-day period in which, for each day of that period, the trading price for the notes was less than 98% of the product of the last reported sale price of our common stock and the applicable conversion rate on such trading day. On and after May 15, 2017, until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert their notes at any time, regardless of the foregoing circumstances. Upon a change in control or termination of trading, holders of the notes may require us to repurchase all or a portion of their notes for cash at a repurchase price equal to 100% of the principal amount, plus any accrued and unpaid interest.

[4] This represents the number of shares hypothetically issuable upon conversion of the principal balance of the Convertible Notes at each date; however, as the terms of the Convertible Notes require net share settlement, the aggregate principal amount of the notes will be paid in cash. Amounts due in excess of the principal, if any, may be settled in cash, shares of the Company's common stock or a combination of cash and shares of common stock, at the Company's election.