Fair-Value Measurements (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value Disclosures [Line Items]
(Losses)/gains recognized in income, net	$ 0	$ (600,000)
Liability Derivatives	4,718,000	4,251,000
Interest expense	18,118,000	20,148,000	18,405,000
Credit Agreement [Member]
Fair Value Disclosures [Line Items]
Amount of credit facility	390,000,000
Interest Rate Swap [Member]
Fair Value Disclosures [Line Items]
Interest expense	1,700,000	1,900,000
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member]
Fair Value Disclosures [Line Items]
Liability Derivatives	4,718,000	4,251,000
Interest Rate Swap [Member] | Credit Agreement [Member]
Fair Value Disclosures [Line Items]
Notional amount	$ 105,000,000
Fixed interest rate in swap	2.04%
Interest Rate Swap [Member] | Credit Agreement [Member] | Minimum [Member]
Fair Value Disclosures [Line Items]
Credit spread	2.00%
Interest Rate Swap [Member] | Credit Agreement [Member] | Maximum [Member]
Fair Value Disclosures [Line Items]
Credit spread	2.75%