Condensed Statements of Comprehensive Income (unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Condensed Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 45,585	$ 36,159
Other comprehensive income (loss):
Foreign currency translation adjustments	(4,421)	745
Income tax benefit (expense)	7	(4)
Foreign currency translation adjustments, net of tax	(4,414)	741
Unrealized gains on investments:
Unrealized gains arising during period	67	152
Less: reclassification adjustments for (losses) included in net income	0	(1)
Changes in unrealized gains on investments	67	153
Income tax benefit (expense)	44	(51)
Unrealized gains on investments, net of tax	111	102
Changes in employee benefit related items:
Amortization of prior service cost	0	(458)
Recognized actuarial gain	133	159
Changes in employee benefit related items	133	(299)
Income tax expense	(23)	(7)
Employee benefit related items, net of tax	110	(306)
Other comprehensive (loss) income	(4,193)	537
Comprehensive income	$ 41,392	$ 36,696