Share-Based Compensation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 1,637	$ 1,360	$ 2,854	$ 2,293
Income tax benefit	(591)	(480)	(1,031)	(801)
Total share-based compensation, net of income tax benefit	1,046	880	1,823	1,492
Restricted stock/performance-based restricted stock (PBRS) [Member]
Summary of share-based compensation expense
Share-based compensation before income tax benefit	971	937	1,720	1,615
Performance unit incentive plan (PUP) [Member]
Summary of share-based compensation expense
Share-based compensation before income tax benefit	434	194	672	259
Stock options [Member]
Summary of share-based compensation expense
Share-based compensation before income tax benefit	153	183	302	330
Restricted Stock Units and Performance Based Restricted Stock Units [Member]
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 79	$ 46	$ 160	$ 89