Condensed Statements of Comprehensive Income (unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Condensed Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 38,231	$ 26,699
Other comprehensive income (loss):
Foreign currency translation adjustments	(3,878)	683
Income tax (expense)	(6)	0
Foreign currency translation adjustments, net of tax	(3,884)	683
Unrealized gains on investments:
Unrealized gains arising during period	282	264
Less: reclassification adjustments for gains included in net income	0	0
Changes in unrealized gains on investments	282	264
Income tax (expense)	(145)	(113)
Unrealized gains on investments, net of tax	137	151
Changes in employee benefit related items:
Amortization of transition asset	(13)	(13)
Amortization of prior service cost	9	10
Recognized actuarial loss	67	(29)
Changes in employee benefit related items	63	(32)
Income tax (expense)	(35)	0
Employee benefit related items, net of tax	28	(32)
Other comprehensive (loss) income	(3,719)	802
Comprehensive income	$ 34,512	$ 27,501