CONSOLIDATED STATEMENT OF INCOME (LOSS) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Income Statement [Abstract]
Net sales	$ 610,911	[1]	$ 537,482	[1]	$ 498,761	[1]
Cost of sales	376,972		349,782		340,015
Gross margin	233,939		187,700		158,746
Selling and administrative expenses	125,244		106,398		99,689
Research and development expenses	22,878		21,646		19,311
Restructuring and impairment charges	5,390		10,376		14,082
Operating income (loss)	80,427		49,280		25,664
Equity income in unconsolidated joint ventures	4,123		4,326		4,743
Other income (expense), net	(1,194)		(1,240)		(208)
Realized investment gain (loss):
Increase (decrease) in fair value of investments	0		0		(522)
Less: Portion reclassified to/from other comprehensive income	0		0		2,723
Net realized gain (loss)	0		0		(3,245)
Interest income (expense), net	(2,946)		(3,481)		(4,304)
Income (loss) before income taxes	80,410		48,885		22,650
Income tax expense (benefit)	27,527		11,226		(46,484)
Income (loss) from continuing operations	52,883		37,659		69,134
Income (loss) from discontinued operations, net of income taxes	0		102		(449)
Net income (loss)	$ 52,883		$ 37,761		$ 68,685
Basic net income (loss) per share:
Income (loss) from continuing operations (in dollars per share)	$ 2.91		$ 2.19		$ 4.21
Income (loss) from discontinued operations (in dollars per share)	$ 0.00		$ 0.01		$ (0.03)
Net income (loss) (in dollars per share)	$ 2.91		$ 2.20		$ 4.18
Diluted net income (loss) per share:
Income (loss) from continuing operations (in dollars per share)	$ 2.83		$ 2.12		$ 4.07
Income (loss) from discontinued operations (in dollars per share)	$ 0.00		$ 0.01		$ (0.03)
Net income (loss) (in dollars per share)	$ 2.83		$ 2.13		$ 4.04
Shares used in computing:
Basic net income per share	18,177,178		17,197,840		16,426,209
Diluted net income per share	18,697,778		17,768,075		16,991,158

[1] Net sales are allocated to countries based on the location of the customer.