Income Taxes - Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015
Income Taxes
NOL and capital loss carryforwards	$ 43,038	$ 67,505
Tax credit carryforwards	27,406	24,954
Estimated liabilities	23,439	19,240
Stock-based compensation	5,480	5,903
Debt repurchase premium	5,635	5,154
Reserves and allowances	3,708	2,469
Other	549	3,176
Valuation allowances	(10,354)	(10,146)
Total deferred tax assets	98,901	118,255
Property, plant and equipment basis differences	(18,630)	(15,797)
Goodwill and intangible asset basis differences	(12,212)	(9,606)
Total deferred tax liabilities	(30,842)	(25,403)
Net deferred tax asset	$ 68,059	$ 92,852