CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Revenues	$ 338,207	$ 321,976	$ 979,616	$ 989,870
Cost of revenues	263,662	247,070	794,504	752,477
Research and development expenses	7,509	23,146	21,773	78,470
Selling, general and administrative expenses	33,776	26,154	91,837	75,904
Income from operations	33,260	25,606	71,502	83,019
Interest income and other, net	672	230	12,465	1,272
Interest expense	(1,082)	(1,143)	(3,292)	(3,438)
Income before income taxes	32,850	24,693	80,675	80,853
Income tax provision	(11,650)	(9,141)	(29,131)	(29,421)
Net income	21,200	15,552	51,544	51,432
Basic income per share	$ 0.35	$ 0.26	$ 0.85	$ 0.85
Diluted income per share	$ 0.35	$ 0.26	$ 0.85	$ 0.85
Net income	21,200	15,552	51,544	51,432
Other comprehensive income (loss):
Defined benefit plans, net of tax of $(213), $163, $(237) and $121, respectively	(339)	258	(372)	191
Unrealized gain (loss) on investments	0	(200)	0	400
Net gain (loss) on foreign exchange derivative instruments, net of tax of $0, $(239), $206 and $59, respectively	0	(383)	326	91
Total other comprehensive income (loss)	(339)	(325)	(46)	682
Comprehensive Income	$ 20,861	$ 15,227	$ 51,498	$ 52,114