Earnings Per Share Calculations (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share Calculations
Stock split ratio	2
Outstanding anti-dilutive SARs (in shares)		361,356	361,356	361,356	361,356
Net income available to common stockholders		$ 12,190	$ 10,381	$ 14,909	$ 12,399
Weighted average common shares, basic (in shares)		41,752,000	41,606,000	41,724,000	41,582,000
Dilutive common stock options (treasury method) (in shares)		16,000	30,000	16,000	30,000
Shares used for dilutive computation (in shares)		41,768,000	41,636,000	41,740,000	41,612,000
Net income per share - basic (in dollars per share)		$ 0.29	$ 0.25	$ 0.36	$ 0.30
Net income per share - diluted (in dollars per share)		$ 0.29	$ 0.25	$ 0.36	$ 0.30