Segment Information (U.S. Government Related Sales by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment, Reporting Information [Line Items]
Net sales	$ 719,359	$ 588,117	$ 548,249	$ 470,148	$ 606,788	$ 548,622	$ 500,381	$ 442,894	$ 2,325,873	$ 2,098,685	$ 2,023,078
Aerospace [Member]
Segment, Reporting Information [Line Items]
Net sales	461,128	404,612	386,343	305,905	399,141	355,992	320,526	266,680	1,557,988	1,342,339	1,233,176
Industrial [Member]
Segment, Reporting Information [Line Items]
Net sales	$ 258,231	$ 183,505	$ 161,906	$ 164,243	$ 207,647	$ 192,630	$ 179,855	$ 176,214	767,885	756,346	789,902
U.S. Government Related [Member]
Segment, Reporting Information [Line Items]
Net sales									$ 524,843	$ 483,761	$ 430,373
Percentage of total attributable to major customer									23.00%	23.00%	21.00%
U.S. Government Related [Member] | Aerospace [Member]
Segment, Reporting Information [Line Items]
Net sales									$ 513,638	$ 469,221	$ 413,978
U.S. Government Related [Member] | Industrial [Member]
Segment, Reporting Information [Line Items]
Net sales									11,205	14,540	16,395
Indirect Sales to U.S. Government [Member]
Segment, Reporting Information [Line Items]
Net sales									$ 438,044	$ 373,350	$ 320,797
Percentage of total attributable to major customer									19.00%	18.00%	16.00%
Indirect Sales to U.S. Government [Member] | Aerospace [Member]
Segment, Reporting Information [Line Items]
Net sales									$ 429,386	$ 362,536	$ 310,952
Indirect Sales to U.S. Government [Member] | Industrial [Member]
Segment, Reporting Information [Line Items]
Net sales									8,658	10,814	9,845
Direct Sales to U.S. Government [Member]
Segment, Reporting Information [Line Items]
Net sales									$ 86,799	$ 110,411	$ 109,576
Percentage of total attributable to major customer									4.00%	5.00%	5.00%
Direct Sales to U.S. Government [Member] | Aerospace [Member]
Segment, Reporting Information [Line Items]
Net sales									$ 84,252	$ 106,685	$ 103,026
Direct Sales to U.S. Government [Member] | Industrial [Member]
Segment, Reporting Information [Line Items]
Net sales									$ 2,547	$ 3,726	$ 6,550
Sales [Member] | General Electric [Member]
Segment, Reporting Information [Line Items]
Percentage of total attributable to major customer									16.00%	16.00%	17.00%
Trade Accounts Receivable [Member] | U.S. Government Related [Member]
Segment, Reporting Information [Line Items]
Percentage of total attributable to major customer									3.00%	3.00%
Trade Accounts Receivable [Member] | General Electric [Member]
Segment, Reporting Information [Line Items]
Percentage of total attributable to major customer									8.00%	10.00%