Supplemental Executive Retirement Plan (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Supplemental Executive Retirement Plan Disclosure
Balance in the Rabbi Trust at the end of the period	$ 5,123		$ 5,123		$ 5,122
Supplemental Executive Retirement Plan (SERP)
Supplemental Executive Retirement Plan Disclosure
Balance in the Rabbi Trust at the end of the period	5,100		5,100		5,100
Components of the periodic benefit cost
Service cost	1,079	988	3,176	2,700
Interest cost	352	248	1,004	635
Amortization of prior service costs	207	90	566	163
Amortization of net actuarial loss	20	32	71	87
Net pension expense	$ 1,658	$ 1,358	$ 4,817	$ 3,585