SUBSEQUENT EVENTS	12 Months Ended
Sep. 30, 2018
SUBSEQUENT EVENTS [Abstract]
SUBSEQUENT EVENTS	20. SUBSEQUENT EVENTS On August 14, 2018, we entered into a Merger Agreement with KMG and the Merger Sub, providing for the acquisition of KMG by Cabot Microelectronics. The Merger Agreement provides that, upon the terms and subject to the satisfaction or valid waiver of the conditions set forth in the Merger Agreement, Merger Sub will merge with and into KMG, with KMG continuing as the surviving corporation and a wholly owned subsidiary of Cabot Microelectronics. The Merger Agreement and the Acquisition were unanimously approved by the board of directors of each of Cabot Microelectronics and KMG. At the effective time of the Acquisition, each outstanding share of KMG common stock, par value $0.01 per share ("KMG Common Stock"), other than shares owned by KMG, Cabot Microelectronics and their subsidiaries, dissenting shares, or shares subject to a KMG Equity Award (as defined below), will automatically be converted into the right to receive the following Merger Consideration, without interest: $55.65 in cash (the "Cash Consideration"); and, 0.2000 shares of common stock of Cabot Microelectronics, par value $0.001 per share ("CMC Common Stock"). Based on the closing price of CMC Common Stock on November 9, 2018, the most recent practicable date prior to the date of this Report on Form 10-K, the Merger Consideration is approximately $1.5 billion, which will fluctuate as the market price of CMC Common Stock fluctuates because a portion of the Merger Consideration is payable in a fixed number of shares of CMC Common Stock. As a result, the value of the Merger Consideration upon completion of the Acquisition could be greater than, less than or the same as the value of the Merger Consideration on the date of this report. Cabot Microelectronics and KMG have each made customary representations, warranties and covenants in the Merger Agreement. The Merger Agreement contains certain customary termination rights by either Cabot Microelectronics or KMG, including if the Acquisition is not consummated by February 14, 2019. If the Merger Agreement is terminated under certain circumstances, KMG will be obligated to pay to Cabot Microelectronics a termination fee equal to $38.8 million in cash. Immediately prior to closing, each restricted stock unit award relating to shares of KMG Common Stock (each, a "KMG Equity Award") granted prior to August 14, 2018 will vest (with any applicable performance targets deemed satisfied at the level specified in the applicable award agreement) and be cancelled in exchange for the Merger Consideration in respect of each share of KMG Common Stock underlying the applicable KMG Equity Award. Each KMG Equity Award granted on or following August 14, 2018 will be converted into a corresponding award relating to shares of CMC Common Stock and continue to vest post-closing in accordance with the terms of the applicable award agreement (which will include vesting on a qualifying termination of employment). The consummation of the Acquisition is subject to customary closing conditions, including the adoption of the Merger Agreement by KMG's shareholders, the meeting for which is scheduled to occur on November 13, 2018. Assuming such conditions are satisfied or validly waived, we expect the Acquisition to close in approximately mid-November 2018. On August 14, 2018, in connection with the execution of the Merger Agreement, we entered into a commitment letter, dated as of August 14, 2018 (the "Commitment Letter"), with JPMorgan Chase Bank, N.A., Bank of America, N.A. and Goldman Sachs Bank USA (together with the additional commitment parties described below, the "Commitment Parties") and Merrill Lynch, Pierce, Fenner & Smith Incorporated, pursuant to which the Commitment Parties have committed to arrange and provide, subject to the terms and conditions of the Commitment Letter, a senior secured revolving credit facility in an aggregate principal amount of up to $200.0 million (the "New Revolving Facility") and a senior secured term loan facility in an aggregate principal amount of up to $1,065.0 million (the "New Term Loan Facility", and together with the New Revolving Facility, the "New Credit Facilities"). On September 4, 2018, we amended and restated the commitment letter to add BMO Harris Financing, Inc., U.S. Bank, National Association, HSBC Bank USA, N.A., and PNC Bank, National Association as additional commitment parties. On November 1, 2018, we completed the syndication of the New Credit Facilities. We expect the New Credit Facilities to be made available pursuant to a credit agreement to be entered into on the closing date of the Acquisition. We expect the New Revolving Facility to mature five years after the closing date of the Acquisition and the New Term Loan Facility to mature seven years after the closing date of the Acquisition and to amortize in equally quarterly installments of 0.25% of the initial principal amount. We expect that the New Credit Facilities will be guaranteed by KMG and all of CMC's and KMG's wholly-owned domestic subsidiaries and will be secured by first priority liens and security interests in substantially all assets of CMC and each guarantor, in each case subject to certain exceptions. We expect borrowings under the New Term Loan Facility to bear interest at LIBOR plus 2.25% per annum and borrowings under the New Revolving Facility to bear interests at a rate per annum equal to LIBOR plus an applicable margin of 1.00% to 1.75% depending on our consolidated leverage ratio. We also expect to be required to pay certain fees and expenses in connection with the New Credit Facility, including an undrawn commitment fee of 0.175% to 0.30% per annum based on our consolidated leverage ratio. We expect that the New Credit Facilities will require us to comply with customary affirmative and negative covenants and events of default, and that the New Revolving Facility will require us to maintain a first lien secured net leverage ratio no greater than 4.00 to 1.00. Although the syndication of the New Credit Facilities is complete, we have not yet entered into definitive documentation with respect to the New Credit Facilities. Accordingly, the terms of the New Credit Facilities may vary from those described herein.

20. SUBSEQUENT EVENTS

On August 14, 2018, we entered into a Merger Agreement with KMG and the Merger Sub, providing for the acquisition of KMG by Cabot Microelectronics. The Merger Agreement provides that, upon the terms and subject to the satisfaction or valid waiver of the conditions set forth in the Merger Agreement, Merger Sub will merge with and into KMG, with KMG continuing as the surviving corporation and a wholly owned subsidiary of Cabot Microelectronics. The Merger Agreement and the Acquisition were unanimously approved by the board of directors of each of Cabot Microelectronics and KMG. At the effective time of the Acquisition, each outstanding share of KMG common stock, par value $0.01 per share ("KMG Common Stock"), other than shares owned by KMG, Cabot Microelectronics and their subsidiaries, dissenting shares, or shares subject to a KMG Equity Award (as defined below), will automatically be converted into the right to receive the following Merger Consideration, without interest: $55.65 in cash (the "Cash Consideration"); and, 0.2000 shares of common stock of Cabot Microelectronics, par value $0.001 per share ("CMC Common Stock"). Based on the closing price of CMC Common Stock on November 9, 2018, the most recent practicable date prior to the date of this Report on Form 10-K, the Merger Consideration is approximately $1.5 billion, which will fluctuate as the market price of CMC Common Stock fluctuates because a portion of the Merger Consideration is payable in a fixed number of shares of CMC Common Stock. As a result, the value of the Merger Consideration upon completion of the Acquisition could be greater than, less than or the same as the value of the Merger Consideration on the date of this report. Cabot Microelectronics and KMG have each made customary representations, warranties and covenants in the Merger Agreement. The Merger Agreement contains certain customary termination rights by either Cabot Microelectronics or KMG, including if the Acquisition is not consummated by February 14, 2019. If the Merger Agreement is terminated under certain circumstances, KMG will be obligated to pay to Cabot Microelectronics a termination fee equal to $38.8 million in cash.

Immediately prior to closing, each restricted stock unit award relating to shares of KMG Common Stock (each, a "KMG Equity Award") granted prior to August 14, 2018 will vest (with any applicable performance targets deemed satisfied at the level specified in the applicable award agreement) and be cancelled in exchange for the Merger Consideration in respect of each share of KMG Common Stock underlying the applicable KMG Equity Award. Each KMG Equity Award granted on or following August 14, 2018 will be converted into a corresponding award relating to shares of CMC Common Stock and continue to vest post-closing in accordance with the terms of the applicable award agreement (which will include vesting on a qualifying termination of employment).

The consummation of the Acquisition is subject to customary closing conditions, including the adoption of the Merger Agreement by KMG's shareholders, the meeting for which is scheduled to occur on November 13, 2018. Assuming such conditions are satisfied or validly waived, we expect the Acquisition to close in approximately mid-November 2018.

On August 14, 2018, in connection with the execution of the Merger Agreement, we entered into a commitment letter, dated as of August 14, 2018 (the "Commitment Letter"), with JPMorgan Chase Bank, N.A., Bank of America, N.A. and Goldman Sachs Bank USA (together with the additional commitment parties described below, the "Commitment Parties") and Merrill Lynch, Pierce, Fenner & Smith Incorporated, pursuant to which the Commitment Parties have committed to arrange and provide, subject to the terms and conditions of the Commitment Letter, a senior secured revolving credit facility in an aggregate principal amount of up to $200.0 million (the "New Revolving Facility") and a senior secured term loan facility in an aggregate principal amount of up to $1,065.0 million (the "New Term Loan Facility", and together with the New Revolving Facility, the "New Credit Facilities"). On September 4, 2018, we amended and restated the commitment letter to add BMO Harris Financing, Inc., U.S. Bank, National Association, HSBC Bank USA, N.A., and PNC Bank, National Association as additional commitment parties.

On November 1, 2018, we completed the syndication of the New Credit Facilities. We expect the New Credit Facilities to be made available pursuant to a credit agreement to be entered into on the closing date of the Acquisition. We expect the New Revolving Facility to mature five years after the closing date of the Acquisition and the New Term Loan Facility to mature seven years after the closing date of the Acquisition and to amortize in equally quarterly installments of 0.25% of the initial principal amount. We expect that the New Credit Facilities will be guaranteed by KMG and all of CMC's and KMG's wholly-owned domestic subsidiaries and will be secured by first priority liens and security interests in substantially all assets of CMC and each guarantor, in each case subject to certain exceptions. We expect borrowings under the New Term Loan Facility to bear interest at LIBOR plus 2.25% per annum and borrowings under the New Revolving Facility to bear interests at a rate per annum equal to LIBOR plus an applicable margin of 1.00% to 1.75% depending on our consolidated leverage ratio. We also expect to be required to pay certain fees and expenses in connection with the New Credit Facility, including an undrawn commitment fee of 0.175% to 0.30% per annum based on our consolidated leverage ratio. We expect that the New Credit Facilities will require us to comply with customary affirmative and negative covenants and events of default, and that the New Revolving Facility will require us to maintain a first lien secured net leverage ratio no greater than 4.00 to 1.00. Although the syndication of the New Credit Facilities is complete, we have not yet entered into definitive documentation with respect to the New Credit Facilities. Accordingly, the terms of the New Credit Facilities may vary from those described herein.