Accumulated Other Comprehensive Income (Loss) (Reclassification) (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Reclassification out of Accumulated Other Comprehensive Income [Line Items]    
Other income (expense), net $ (129) $ (1,191)
Income before income tax expense 19,884 20,495
Income tax benefit (expense) (6,257) (5,915)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized gains and losses on marketable securities[Member]    
Reclassification out of Accumulated Other Comprehensive Income [Line Items]    
Other income (expense), net   323
Income tax benefit (expense)   (113)
Net income (loss)   210
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized gain (loss) on derivative instruments [Member]    
Reclassification out of Accumulated Other Comprehensive Income [Line Items]    
Other income (expense), net 145  
Income tax benefit (expense) (51)  
Net income (loss) 94  
Reclassification out of Accumulated Other Comprehensive Income [Member] | Amortization of defined benefit pension and other post-retirement benefit items [Member]    
Reclassification out of Accumulated Other Comprehensive Income [Line Items]    
Actuarial losses 412 [1] 214 [1]
Income before income tax expense 412 214
Income tax benefit (expense) (144) (75)
Net income (loss) $ 268 $ 139
[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost. See Note 9 - "Pension Benefits and Other Postretirement Benefit Plans" for additional details.