CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income and Comprehensive Income [Abstract]
Net income	$ 53,760	$ 66,040	$ 129,252	$ 219,055
Other comprehensive income (loss), net of taxes:
Pension adjustment	125	106	372	318
Foreign currency translation	214	213	(413)	195
Unrealized gain (loss) on securities and reclassification adjustments	28	3	(2)	(118)
Comprehensive income	$ 54,127	$ 66,362	$ 129,209	$ 219,450