American Railcar Industries (NASDAQ: ARII) has launched a buyout offer for Greenbrier Companies (GBX -1.68%), according to an SEC filing. American Railcar, whose chairman is activist investor Carl Icahn, is offering $20 in cash per share of common stock for the rival train car manufacturer.

Icahn held slightly less than 10% of Greenbrier at the end of November. This made him the firm's top shareholder at the time.

The $20 bid represents a premium of 5% to Greenbrier's Monday closing price. The bid values Greenbrier at slightly less than $543 million.

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