Income Taxes - Deferred Tax Assets and Liabilities (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 64,199,000	$ 59,501,000
Decreased in valuation allowance	4,700,000
Operating loss carryforwards, federal	157,700,000
Operating loss carryforwards, state	64,600,000
Tax credit carryforwards research and development and other, federal	5,100,000
Tax credit carryforwards research and development and other, state	6,600,000
Excess tax benefits from employee stock purchase plan	4,100,000	3,400,000
Decrease in foreign tax	665,000	733,000
Benefit of the tax holiday on net income per share (diluted)	$ 0.02	$ 0.03
Unremitted earnings from foreign subsidiaries	39,200,000
Total unrecognized tax benefits				11,700,000
Interest and penalties	34,000	126,000
Repatriation of Foreign Earnings, Amount	1,590,000	0	0
Deferred tax assets:
Tax loss carryforwards	54,551,000	55,109,000
Tax credit carryforwards	19,000	19,000
Uniform capitalization, contract and inventory related reserves	1,728,000	1,493,000
Accrued vacation	669,000	632,000
Stock-based compensation	1,428,000	1,235,000
Intangible assets	1,364,000	1,032,000
Deferred revenue	149,000	179,000
Unrealized gains and losses	1,780,000	0
Other	2,668,000	1,721,000
Total	64,356,000	61,420,000
Deferred tax liabilities:
Inventory deduction	(206,000)	(290,000)
Pension assets	(1,476,000)	(2,125,000)
Allowance for doubtful accounts	(407,000)	(405,000)
Tax basis depreciation less book depreciation	(192,000)	(1,989,000)
Withholding tax on undistributed earnings of foreign subsidiary	(1,590,000)	0
Other	(241,000)	(1,000)
Total	(4,112,000)	(4,810,000)
Net deferred tax assets before valuation allowance	60,244,000	56,610,000
Valuation allowance	(64,199,000)	(59,501,000)
Net deferred tax liabilities	(3,955,000)	(2,891,000)
Undistributed Earnings Of Domestic Subsidiaries Not Considered Indefinitely Reinvested	31,800,000
Deferred tax asset stock option deductions [Member]
Operating Loss Carryforwards [Line Items]
Valuation allowance	15,500,000			15,500,000
Deferred tax liabilities:
Valuation allowance	$ (15,500,000)			$ (15,500,000)