Basis of Presentation and Consolidation (Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	$ 48,212		$ 45,827	$ 69,603		$ 73,796
Income tax provision	(17,480)		(17,356)	(26,559)		(27,597)
Net income	30,732		28,471	43,044		46,199
Defined Benefit Plan Items | Amount Reclassified from Accumulated Other Comprehensive Income
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior-service cost	(136)	[1],[2]		(272)	[1],[2]
Income before income taxes	(136)	[1]		(272)	[1]
Income tax provision	51	[1]		102	[1]
Net income	$ (85)	[1]		$ (170)	[1]

[1] Amounts in parentheses indicate debits to profit/loss.

[2]