Accumulated Other Comprehensive Income Reclassifications in AOCI (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
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	$ 229,789		$ 176,466	$ 421,082		$ 311,261
Provision for income taxes	(83,973)		(60,965)	(151,919)		(107,947)
Net income	145,816		115,501	269,163		203,314
Accumulated Defined Benefit Plans Adjustment | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service costs	(95)	[1]		(190)	[1]
Net loss	(600)	[1]		(1,119)	[1]
Income before income taxes	(695)			(1,309)
Provision for income taxes	268			504
Net income	$ (427)			$ (805)

[1] These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. For additional information, please read Note 8 (Employee Benefits) to the financial statements included in the 2012 Form 10-K.