Condensed Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 42,687	$ 44,134	$ 136,496	$ 123,147
Other comprehensive income (loss):
Foreign currency translation adjustments, before reclassification and tax	(2,329)	(5,354)	(4,014)	(3,205)
Less: reclassification adjustment for gains included in net income upon liquidation	0	0	563	0
Foreign currency translation adjustments, before tax	(2,329)	(5,354)	(4,577)	(3,205)
Income tax benefit (expense)	47	(6)	48	(19)
Foreign currency translation adjustments, net of tax	(2,282)	(5,360)	(4,529)	(3,224)
Unrealized gains (losses) on investments:
Unrealized gains (losses) arising during period	(13)	(12)	(137)	288
Less: reclassification adjustments for gains included in net income	455	2	455	1
Changes in unrealized (losses) gains on investments	(468)	(14)	(592)	287
Income tax benefit (expense)	156	45	258	(58)
Unrealized gains on investments, net of tax	(312)	31	(334)	229
Changes in employee benefit related items:
Amortization of prior service cost	0	(462)	0	(1,377)
Recognized actuarial gain	407	152	584	446
Changes in employee benefit related items	407	(310)	584	(931)
Income tax (expense) benefit	(11)	7	(35)	4
Employee benefit related items, net of tax	396	(303)	549	(927)
Other comprehensive (loss)	(2,198)	(5,632)	(4,314)	(3,922)
Comprehensive income	$ 40,489	$ 38,502	$ 132,182	$ 119,225