Consolidated Statements of Changes in Equity and Comprehensive Income Statement (USD $)	Total	Class A Common Stock [Member]	Class B Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Noncontrolling Interests [Member]
BALANCE, at Dec. 31, 2008	$ 479,414,000	$ 458,000	$ 26,000	$ 214,356,000	$ 479,598,000	$ (14,033,000)	$ (202,342,000)	$ 1,351,000
Net income	61,473,000	0	0	0	61,327,000	0	0	146,000
Currency translation adjustments	29,378,000	0	0	0	0	29,378,000	0	0
Fair market value adjustments of cash flow hedges	3,991,000	0	0	0	0	3,991,000	0	0
Pension and post-retirement medical adjustment	147,000	0	0	0	0	147,000	0	0
Comprehensive Income	94,989,000
Proceeds from employee stock purchases	5,765,000	5,000	0	5,760,000	0	0	0	0
Compensation cost related to equity awards	6,031,000	0	0	6,031,000	0	0	0	0
Excess tax benefits from share-based compensation	1,152,000	0	0	1,152,000	0	0	0	0
Stock issuance proceeds, net of stock issuance costs	106,614,000	46,000	0	106,568,000	0	0	0	0
Change in ownership of noncontrolling interest	(4,360,000)	0	0	(3,157,000)	0	0	0	(1,203,000)
Sale of investment in Bolivia	(294,000)	0	0	0	0	0	0	(294,000)
Treasury stock acquisitions	(434,000)	0	0	0	0	0	(434,000)	0
BALANCE, at Dec. 31, 2009	688,877,000	509,000	26,000	330,710,000	540,925,000	19,483,000	(202,776,000)	0
Net income	81,260,000	0	0	0	81,260,000	0	0	0
Currency translation adjustments	21,877,000	0	0	0	0	21,877,000	0	0
Fair market value adjustments of cash flow hedges	(1,590,000)	0	0	0	0	(1,590,000)	0	0
Pension and post-retirement medical adjustment	344,000					344,000	0	0
Comprehensive Income	101,891,000
Proceeds from employee stock purchases	18,205,000	8,000	0	18,197,000	0	0	0	0
Conversion of Class B common stock to Class A common stock	0	2,000	(2,000)	0	0	0	0	0
Compensation cost related to equity awards	7,174,000	0	0	7,174,000	0	0	0	0
Excess tax benefits from share-based compensation	1,943,000	0	0	1,943,000	0	0	0	0
Stock issuance proceeds, net of stock issuance costs	0
Change in ownership of noncontrolling interest	0
Treasury stock acquisitions	(850,000)	0	0	0	0	0	(850,000)	0
BALANCE, at Dec. 31, 2010	817,240,000	519,000	24,000	358,024,000	622,185,000	40,114,000	(203,626,000)	0
Net income	119,484,000	0	0	0	119,484,000	0	0	0
Currency translation adjustments	(3,511,000)	0	0	0	0	(3,511,000)	0	0
Fair market value adjustments of cash flow hedges	1,334,000	0	0	0	0	1,334,000	0	0
Pension and post-retirement medical adjustment	(42,000)					(42,000)	0	0
Comprehensive Income	117,265,000
Proceeds from employee stock purchases	17,433,000	6,000	0	17,427,000	0	0	0	0
Conversion of Class B common stock to Class A common stock	0	2,000	(2,000)	0	0	0	0	0
Compensation cost related to equity awards	7,776,000	0	0	7,776,000	0	0	0	0
Excess tax benefits from share-based compensation	2,246,000	0	0	2,246,000	0	0	0	0
Stock issuance proceeds, net of stock issuance costs	0
Change in ownership of noncontrolling interest	0
Treasury stock acquisitions	(1,326,000)	0	0	0	0	0	(1,326,000)	0
BALANCE, at Dec. 31, 2011	$ 960,634,000	$ 527,000	$ 22,000	$ 385,473,000	$ 741,669,000	$ 37,895,000	$ (204,952,000)	$ 0