Stockholders' Equity (Narrative) (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2017	Mar. 31, 2017	Mar. 31, 2016
Payments for repurchases of common stock		$ 61,782	$ 117,820
Total unrecognized compensation cost related to non-vested stock-based compensation arrangements	$ 12,622	$ 12,622
Unrecognized compensation cost is expected to be recognized over a weighted-average period		2 years 3 months 18 days
Forfeiture rate, Board of Directors	0.00%	0.00%
Forfeiture rate, non-Board of Directors	9.00%	9.00%
Stock Options [Member]
Vested contractual term, in years		10 years
Vesting rate		25.00%
Vesting period, in years		4 years
Restricted Stock Award [Member]
Shares granted, Number of Shares	0	0
Restricted stock awards granted		24
Vesting period, in years		4 years
Service period for restricted stock award		4 years
2017 Plan [Member]
Stock-based compensation award conditionally awarded date		Oct. 03, 2016
Stock-based compensation award conditionally awarded date approved		Jan. 25, 2017
Stock-based compensation plan effective date		Sep. 14, 2016
Number of stock shares authorized for grants	2,000	2,000
2016 Authorization [Member]
Authorized repurchase amount	$ 500,000	$ 500,000
Payments for repurchases of common stock		$ 61,229
Repurchase period in years		3 years
Purchases of treasury stock, number of shares		886
10b5-1 Plan [Member]
Authorized repurchase amount			125,000
Payments for repurchases of common stock			$ 119,119
Purchases of treasury stock, number of shares		350	2,523
10b-18 Plan [Member]
Purchases of treasury stock, number of shares		536

Unrecognized cost of unvested share-based compensation awards.

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