Share-Based Compensation Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based compensation expense and income tax benefits recognized during the periods
Share-based compensation expense	$ 18,864	$ 17,423	$ 16,543
Income tax benefit	(6,309)	(5,794)	(5,572)
Share-based compensation expense, net of tax	12,555	11,629	10,971
Summary of compensation expense recognized related to cash awards
Cash awards	1,099	1,882	2,052
Stock option and stock purchase plan [Member]
Share-based compensation expense and income tax benefits recognized during the periods
Share-based compensation expense	9,469	9,497	9,069
Nonvested stock [Member]
Share-based compensation expense and income tax benefits recognized during the periods
Share-based compensation expense	$ 9,395	$ 7,926	$ 7,474