Condensed Statements of Comprehensive Income (unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Condensed Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 42,854	$ 40,276	$ 79,013	$ 78,507
Other comprehensive income (loss):
Foreign currency translation adjustments	1,404	(3,112)	2,149	(6,990)
Income tax (expense) benefit	(9)	(6)	(13)	(12)
Foreign currency translation adjustments, net of tax	1,395	(3,118)	2,136	(7,002)
Unrealized (losses) gains on investments:
Unrealized (losses) gains arising during period	148	(161)	300	121
Less: reclassification adjustments for gains (losses) included in net income	0	3	(1)	3
Changes in unrealized (losses) gains on investments	148	(164)	301	118
Income tax benefit (expense)	(52)	22	(103)	(123)
Unrealized (losses) gains on investments, net of tax	96	(142)	198	(5)
Changes in employee benefit related items:
Amortization of transition asset	0	(5)	0	(18)
Amortization of prior service cost	(457)	10	(915)	19
Recognized actuarial gain (loss)	135	69	294	136
Changes in employee benefit related items	(322)	74	(621)	137
Income tax expense	4	(1)	(3)	(36)
Employee benefit related items, net of tax	(318)	73	(624)	101
Other comprehensive income (loss)	1,173	(3,187)	1,710	(6,906)
Comprehensive income	$ 44,027	$ 37,089	$ 80,723	$ 71,601