Treasury Stock - Narrative (Details) - shares	Sep. 30, 2017	May 31, 2017	Mar. 31, 2017	Sep. 30, 2015	Sep. 30, 2013
Stockholders' Equity Note [Abstract]
Number of shares authorized to be repurchased (up to) (in shares)	7,000,000	2,000,000	5,000,000	170,000	105,000