Share-Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 7,232,000	$ 4,413,000	$ 3,518,000
Income tax benefit	(2,574,000)	(1,594,000)	(1,225,000)
Total share-based compensation, net of income tax benefit	4,658,000	2,819,000	2,293,000
Restricted stock/performance-based restricted stock (PBRS) [Member]
Summary of share-based compensation expense
Share-based compensation before income tax benefit	3,267,000	3,042,000	2,821,000
Performance unit incentive plan (PUP) [Member]
Summary of share-based compensation expense
Share-based compensation before income tax benefit	2,922,000	714,000	(3,000)
Stock options [Member]
Summary of share-based compensation expense
Share-based compensation before income tax benefit	593,000	537,000	447,000
Restricted Stock Units and Performance Based Restricted Stock Units [Member]
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 450,000	$ 120,000	$ 253,000