Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Net income	$ 385,555	$ 258,966	$ 221,393
Pension and other post-retirement benefits liability
Pension and other post-retirement reserves adjustment (excluding amortization)	(4,301)	(6,620)	2,177
Amortization of benefits liability	2,340	1,985	2,277
Income tax provision on pension and other post-retirement benefits liability	753	1,820	(926)
Foreign currency translation adjustments	623	(407)	944
Available-for-sale investments
Unrealized holding gains on investments	14,582	1,848	0
Income tax provision on unrealized holding gains	(5,229)	(663)	0
Reclassification of net realized gain to net income	(10,538)	0	0
Other comprehensive (loss) income	(1,770)	(2,037)	4,472
Comprehensive income	$ 383,785	$ 256,929	$ 225,865