CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement Of Income and Comprehensive Income [Abstract]
Net income	$ 40,416	$ 72,260	$ 75,492	$ 153,015
Other comprehensive income (loss), net of taxes:
Pension adjustment	124	106	248	212
Foreign currency translation	(383)	(119)	(627)	(18)
Unrealized gain (loss) on securities and reclassification adjustments	30	(116)	(31)	(121)
Comprehensive income	$ 40,187	$ 72,131	$ 75,082	$ 153,088