Debt and Bank Borrowing Arrangements; Convertible Note and Common Stock Offerings (Details) (USD $)	12 Months Ended							12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2005	Dec. 31, 2011 2005 LOC [Member]	Dec. 31, 2011 2011 LOC [Member]	Jun. 30, 2011 2011 LOC [Member]	Dec. 31, 2011 Convertible Notes [Member] Decimal	Dec. 31, 2010 Convertible Notes [Member]	Dec. 31, 2009 Convertible Notes [Member]	Dec. 31, 2009 Repurchase of Convertible Notes [Member]
Debt and Bank Borrowing Arrangements; Convertible Note and Common Stock Offerings [Abstract]
Issuance of common stock (in shares)				2,070,000
Equity issuance, per share amount				$ 43.31
Proceeds from offering, net				$ 84,600,000
Payments of stock issuance costs				5,000,000
Issuance of senior subordinated convertible notes				121,000,000
Stated interest rate (in hundredths)				2.875%
Maturity date				Dec. 15, 2035
Extinguishment of Debt [Line Items]
Convertible Notes repurchased											27,900,000
Purchase price of repurchased Notes											23,200,000
Estimated fair value of conversion feature of notes repurchased											21,800,000
Gain recognized on note repurchase											2,300,000
Unamortized debt issuance costs											392,000
Gain on early extinguishment of debt	0	0	1,881,000								1,900,000
Equity component of convertible Notes repurchased, additional paid in capital											1,400,000
Remaining amount of notes authorized for note repurchase program								26,800,000
Notes repurchases - original authorized amount								50,000,000
Interest paid	2,709,000	3,251,000	2,952,000							2,952,000
Repayments of convertible debt	0	0	20,239,000							20,239,000
Long-term debt [Abstract]
Principal amount								93,100,000	93,100,000		24,100,000
Unamortized discount								(3,806,000)	(7,501,000)
Net carrying amount								89,294,000	85,599,000
Current portion of long-term debt								89,294,000	0
Noncurrent portion of long-term debt	0	85,599,000						0	85,599,000
Equity component, net of income tax benefit								16,399,000	16,399,000
Discount rate used on the liability component of long-term debt (in hundredths)								7.50%
Interest expense on Convertible Notes [Abstract]
Contractual interest coupon								2,676,000	2,677,000	3,058,000
Non-cash amortization of discount on the liability component								3,694,000	3,436,000	3,641,000
Non-cash amortization of debt issuance costs								380,000	364,000	399,000
Total	3,695,000	3,436,000	3,643,000					6,750,000	6,477,000	7,098,000
Conversion factor (in shares per $1000 principal)								17.1032
Principal per conversion								1,000
Conversion price (in dollars per share)								$ 58.47
Terms of conversion								The Notes are convertible into 17.1032 shares of Ceradyne's common stock for each $1,000 principal amount of the Notes (which represents a conversion price of approximately $58.47 per share), subject to adjustment. The conversion rate will be adjusted upon the occurrence of events that affect Ceradyne's outstanding common stock, such as the issuance of our common stock or other securities as a dividend distribution to holders of our common stock, a subdivision or combination of our common stock, a recapitalization, reclassification or change of our common stock, or a consolidation or merger involving Ceradyne, as a result of which our common stock would be converted into, or exchanged for, stock, other securities or other property. Generally, the conversion rate would be adjusted as of the effective time of such transaction, such that the Notes would then be convertible into the kind and amount of shares of stock, other securities or other property, that a holder of a number of shares of common stock equal to the conversion rate prior to such transaction would have owned or been entitled to receive upon such transaction. The conversion rate will also be adjusted under certain circumstances to provide for a make whole premium, as described below. The Notes are convertible only under certain circumstances, including (a) during a calendar quarter if the closing price of the Company's common stock for at least twenty trading days in the thirty consecutive trading days ending on the last trading day of the preceding calendar quarter is more than 120% of the then effective conversion price, (b) during the five business day period after any five consecutive trading day period in which the trading price per $1,000 principal amount of Notes for each day of that period was less than 98% of the product of the closing price for our common stock for each day of that period and the then applicable conversion rate, (c) if the Notes are called for redemption, (d) if specified corporate transactions or fundamental changes occur, or (e) during the ten trading days prior to maturity of the Notes. With respect to each $1,000 principal amount of the Notes surrendered for conversion, the Company will deliver the conversion value to holders as follows: (1) an amount in cash equal to the lesser of (a) the aggregate conversion value of the Notes to be converted and (b) $1,000, and (2) if the aggregate conversion value of the Notes to be converted is greater than $1,000, an amount in shares or cash equal to such aggregate conversion value in excess of $1,000.
Put options terms								The Notes contain put options, which may require the Company to repurchase in cash all or a portion of the Notes on December 15, 2012, December 15, 2015, December 15, 2020, December 15, 2025, and December 15, 2030 at a repurchase price equal to 100% of the principal amount of the Notes to be repurchased plus accrued and unpaid interest, including contingent interest (as described below), if any, up to but excluding the repurchase date. The Company reclassified its long term debt consisting of its outstanding Notes, as short-term debt because the Note holders have the right to demand repayment on December 15, 2012.
Terms of interest rate payments								The Company is obligated to pay contingent interest to the holders of the Notes during any six-month period from June 15 to December 14 and from December 15 to June 14, commencing with the six-month period beginning December 20, 2010 and ending on June 14, 2011, if the average trading price of the note for the five trading day period ending on the third trading day immediately preceding the first day of the relevant contingent interest period equals $1,200 (120% of the principal amount of a note) or more. The amount of contingent interest payable per note for any relevant contingent interest period shall equal 0.25% per annum of the average trading price of a note for the five trading day period ending on the third trading day immediately preceding the first day of the relevant contingent interest period. This contingent interest payment feature represents an embedded derivative.
Line of Credit Facility [Line Items]
Unsecured line of credit, maximum borrowing capacity					10,000,000	7,000,000	5,000,000
Borrowings outstanding					0	0
Outstanding letters of credit					4,200,000	1,900,000
Interest rate (in hundredths)					1.30%	1.30%
Basis spread on LIBOR						1.00%
Capitalized interest		$ 445,000
Dividends payable, date declared	Feb. 16, 2012
Dividends declared (in dollars per share)	$ 0.15
Dividends payable, date to be paid	Mar. 20, 2012
Dividends payable, date of record	Mar. 06, 2012