Condensed Statements of Comprehensive Income (unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 36,159	$ 38,231
Other comprehensive income (loss):
Foreign currency translation adjustments	745	(3,878)
Income tax expense	(4)	(6)
Foreign currency translation adjustments, net of tax	741	(3,884)
Unrealized gains (losses) on investments:
Unrealized gains arising during period	152	282
Less: reclassification adjustments for (losses) included in net income	(1)	0
Changes in unrealized gains (losses) on investments	153	282
Income tax expense	(51)	(145)
Unrealized gains (losses) on investments, net of tax	102	137
Changes in employee benefit related items:
Amortization of transition asset	0	(13)
Amortization of prior service cost	(458)	9
Recognized actuarial gain (loss)	159	67
Changes in employee benefit related items	(299)	63
Income tax expense	(7)	(35)
Employee benefit related items, net of tax	(306)	28
Other comprehensive income (loss)	537	(3,719)
Comprehensive income	$ 36,696	$ 34,512