Subsequent Events (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended						9 Months Ended		168 Months Ended				0 Months Ended		3 Months Ended						0 Months Ended
	Aug. 06, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013	Nov. 06, 2013	Oct. 29, 2013	Feb. 05, 2013	Nov. 06, 2013 Subsequent Event [Member]	Aug. 06, 2013 Subsequent Event [Member]	Sep. 30, 2013 Quarterly Dividend [Member]	Jun. 30, 2013 Quarterly Dividend [Member]	Mar. 31, 2013 Quarterly Dividend [Member]	Sep. 30, 2012 Quarterly Dividend [Member]	Jun. 30, 2012 Quarterly Dividend [Member]	Mar. 31, 2012 Quarterly Dividend [Member]	Aug. 06, 2013 Quarterly Dividend [Member] Subsequent Event [Member]
Subsequent Event [Line Items]
Stock repurchased (in shares)														7,000
Average price per share of repurchased shares (in dollars per share)		$ 72.40			$ 47.79			$ 57.97	$ 44.94	$ 41.95				$ 70.24
Shares available to be repurchased (in shares)											986,184		500,000
Shares authorized for issuance (in shares)		1,500,000						1,500,000				2,000,000
Dividends declared (in dollars per share)		$ 0.06			$ 0.30			$ 0.16	$ 0.63							$ 0.06	$ 0.05	$ 0.05	$ 0.05	$ 0.04	$ 0.04	$ 0.06
Special dividend declared (in dollars per share)															$ 0.50
Dividends declared date																						Nov. 06, 2013
Dividends payable date		Sep. 24, 2013	Jun. 25, 2013	Mar. 26, 2013	Sep. 25, 2012	Jun. 26, 2012	Mar. 27, 2012															Dec. 24, 2013
Dividends record date		Sep. 10, 2013	Jun. 11, 2013	Mar. 12, 2013	Sep. 11, 2012	Jun. 12, 2012	Mar. 13, 2012															Dec. 10, 2013
Shareholder-designated contribution (in shares)	0.25
Expected expense related to Shareholder-designated charitable contribution program	$ 5.3
Record date of shareholder contribution	Dec. 31, 2013
Percentage stock based compensation expense recognize over three years vesting period (in hundredths)		30.00%
Stock based compensation expense recognize over five years vesting period		70.00%
Vesting period for recognition of 30 percent of stock based compensation expense		3 years
Vesting period for recognition of 70 percent of stock based compensation expense		5 years