Stockholders' Equity (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stockholders' Equity [Abstract]
Shares purchased under share repurchase plan, shares	4,353,801	3,349,286	3,173,182
Shares purchased under share repurchase plan, value	$ 160,200	$ 102,091	$ 65,445
Preferred Stock, par value	$ 0.01	$ 0.01
Price at which registered holder is entitled to purchase preferred stock	$ 133.33
Minimum percentage of common stock owned by person or group	15.00%
Stockholder Rights, expiration date	Mar. 14, 2012