Segment Information - Financial Information for Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Revenue
Products	$ 160,491	$ 132,613	$ 302,675	$ 254,727
Services	46,769	36,720	93,913	74,561
Total revenue	207,260	169,333	396,588	329,288
Gross profit	84,229	64,524	159,444	121,467
Segment operating income (loss)	23,819	14,801	44,659	27,963
Total assets	1,066,541		1,066,541		$ 766,628
Brooks Semiconductor Solutions Group
Revenue
Products	137,025	115,634	257,228	225,029
Services	21,696	19,031	43,379	36,252
Total revenue	158,721	134,665	300,607	261,281
Gross profit	65,299	51,325	124,752	96,794
Brooks Life Science Systems
Revenue
Products	23,466	16,979	45,447	29,698
Services	25,073	17,689	50,534	38,309
Total revenue	48,539	34,668	95,981	68,007
Gross profit	18,930	13,199	34,692	24,673
Operating Segments
Revenue
Segment operating income (loss)	33,519	21,293	59,741	38,776
Depreciation expense	3,172	2,364	5,870	4,730
Total assets	738,679		738,679		632,074
Operating Segments | Brooks Semiconductor Solutions Group
Revenue
Segment operating income (loss)	30,836	20,003	57,198	37,374
Depreciation expense	1,133	1,319	2,282	2,595
Total assets	353,654		353,654		325,408
Operating Segments | Brooks Life Science Systems
Revenue
Segment operating income (loss)	2,683	1,290	2,543	1,402
Depreciation expense	2,039	$ 1,045	3,588	$ 2,135
Total assets	$ 385,025		$ 385,025		$ 306,666