Accumulated Other Comprehensive Income (Loss) (Reclassification) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net		$ (517)	$ (76)	$ (646)	$ (1,268)
Income before income tax expense		19,081	16,485	38,965	36,980
Tax benefit (expense)		(5,541)	(5,583)	(11,798)	(11,498)
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		(190)		144
Tax benefit (expense)		66		(50)
Net of tax		(124)		94
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			(1)		322
Tax benefit (expense)			0		(113)
Net of tax			(1)		209
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	[1]	403	191	817	405
Income before income tax expense		403	191	817	405
Tax benefit (expense)		(141)	(67)	(286)	(142)
Net of tax		$ 262	$ 124	$ 531	$ 263

[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.