Summary of Company's Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Sales	$ 68,551	$ 76,420	$ 169,899	$ 154,171
Total income (loss) from operations	15,956	25,556	51,623	57,104
Seismic
Segment Reporting Information [Line Items]
Sales	63,703	69,758	158,930	141,842
Total income (loss) from operations	19,473	27,842	58,016	61,803
Non-Seismic
Segment Reporting Information [Line Items]
Sales	4,795	6,444	10,707	11,911
Total income (loss) from operations	263	892	1,037	1,357
Corporate
Segment Reporting Information [Line Items]
Sales	53	218	262	418
Total income (loss) from operations	$ (3,780)	$ (3,178)	$ (7,430)	$ (6,056)