Condensed Statements of Comprehensive Income (unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Condensed Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 44,134	$ 29,523	$ 123,147	$ 108,030
Other comprehensive (loss) income:
Foreign currency translation adjustments	(5,354)	3,540	(3,205)	(3,450)
Income tax (expense) benefit	(6)	226	(19)	214
Foreign currency translation adjustments, net of tax	(5,360)	3,766	(3,224)	(3,236)
Unrealized (losses) gains on investments:
Unrealized (losses) gains arising during period	(12)	(86)	288	35
Less: reclassification adjustments for gains (losses) included in net income	2	(1)	1	2
Changes in unrealized (losses) gains on investments	(14)	(85)	287	33
Income tax benefit (expense)	45	47	(58)	(76)
Unrealized (losses) gains on investments, net of tax	31	(38)	229	(43)
Changes in employee benefit related items:
Amortization of transition asset	0	0	0	(18)
Amortization of prior service cost	(462)	(282)	(1,377)	(263)
Recognized actuarial gain	152	1,808	446	1,944
Changes in employee benefit related items	(310)	1,526	(931)	1,663
Income tax benefit (expense)	7	(21)	4	(57)
Employee benefit related items, net of tax	(303)	1,505	(927)	1,606
Other comprehensive (loss) income	(5,632)	5,233	(3,922)	(1,673)
Comprehensive income	$ 38,502	$ 34,756	$ 119,225	$ 106,357