Stock-Based Compensation - Expense & Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Common-stock based award plan
Compensation expense (in dollars)	$ 6,066		$ 6,097	$ 13,987	$ 13,079
Stock options
Common-stock based award plan
The period from the grant date after which options expire				10 years
Compensation expense (in dollars)	$ 1,776		1,908	$ 5,326	$ 4,970
Weighted-average assumptions utilized in determining the fair value of options
Risk-free interest rate (as a percent)				1.80%	1.70%
Expected stock volatility (as a percent)				37.60%	36.90%
Dividend yield (as a percent)				4.60%	3.90%
Expected term				5 years 6 months	5 years 6 months
Options
Options outstanding at the beginning of the period (in shares)	3,531,000	2,776,000		2,776,000
Granted (in shares)	0			876,379
Exercised (in shares)	(61,000)			(180,000)
Forfeited/Expired (in shares)	(14,000)			(16,000)
Option outstanding at the end of the period (in shares)	3,456,000	3,531,000		3,456,000
Vested and expected to vest at the end of the period (in shares)	3,411,000			3,411,000
Exercisable at the end of the period (in shares)	2,270,000			2,270,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 51.51	$ 48.51		$ 48.51
Granted (in dollars per share)	58.25			58.25
Exercised (in dollars per share)	30.94			31.10
Forfeited/Expired (in dollars per share)	58.25			57.74
Outstanding at the end of the period (in dollars per share)	51.85	51.51		51.85
Vested and expected to vest at the end of the period (in dollars per share)	51.74			51.74
Exercisable at the end of the period (in dollars per share)	$ 46.46			$ 46.46
Weighted- Average Remaining Contractual Term
Outstanding at the end of the period	6 years 2 months 12 days
Vested and expected to vest at the end of the period	6 years 2 months 12 days
Exercisable at the end of the period	4 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 31,600			$ 31,600
Vested and expected to vest at the end of the period (in dollars)	31,600			31,600
Exercisable at the end of the period (in dollars)	31,600			31,600
Weighted-average fair value of options granted (in dollars per share)		$ 13.12
Total intrinsic value of options exercised (in dollars)	1,900			5,100
Unrecognized compensation cost (in dollars)	10,800			$ 10,800
Weighted-average period over which unrecognized compensation cost is expected to be recognized				3 years 2 months 12 days
Restricted stock
Common-stock based award plan
Granted (in shares)				294,575
Compensation expense (in dollars)	4,290		$ 4,189	$ 8,661	$ 8,109
Aggregate Intrinsic Value
Unrecognized compensation cost (in dollars)	$ 28,500			$ 28,500
Weighted-average period over which unrecognized compensation cost is expected to be recognized				2 years 8 months 12 days
Restricted stock | Minimum
Common-stock based award plan
Vesting period				3 years
Restricted stock | Maximum
Common-stock based award plan
Vesting period				6 years