Condensed Statements of Shareholders' Equity (USD $) In Millions, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2012	$ 998.4	$ 80.2	$ 856.1	$ (371.3)	$ 433.4
Balance (in shares) at Dec. 31, 2012		80.2
Net income	40.5	0	0	0	40.5
Other comprehensive income	0.2	0	0	0.2	0
Dividends paid:
Common stock ($0.20 per share)	(16.0)	0	0	0	(16.0)
Common stock repurchased and retired (in shares)	(0.2)	(0.2)
Common stock repurchased and retired	(4.6)	(0.2)	(4.4)	0	0
Common stock issued for:
Stock options exercised (in shares)	0.3	0.3
Stock options exercised	4.7	0.3	4.4	0	0
Other Transactions (Shares)		0
Other Transactions	1.0	0	1.0	0	0
Stock-based compensation	0.4	0	0.4	0	0
Balance at Mar. 31, 2013	1,024.6	80.3	857.5	(371.1)	457.9
Balance (in shares) at Mar. 31, 2013		80.3
Balance at Dec. 31, 2013	1,101.1	79.4	838.8	(365.1)	548.0
Balance (in shares) at Dec. 31, 2013		79.4
Net income	29.5	0	0	0	29.5
Other comprehensive income	1.6	0	0	1.6	0
Dividends paid:
Common stock ($0.20 per share)	(15.9)	0	0	0	(15.9)
Common stock repurchased and retired (in shares)	(0.6)	(0.6)
Common stock repurchased and retired	(14.7)	(0.6)	(14.1)	0	0
Common stock issued for:
Stock options exercised (in shares)	0.2	0.2
Stock options exercised	5.3	0.2	5.1	0	0
Other Transactions (Shares)		0
Other Transactions	(1.0)	0	(1.0)	0	0
Stock-based compensation	1.7	0	1.7	0	0
Balance at Mar. 31, 2014	$ 1,107.6	$ 79.0	$ 830.5	$ (363.5)	$ 561.6
Balance (in shares) at Mar. 31, 2014		79.0