Acquisitions Schedule of Unaudited Pro Forma Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Business Acquisition, Pro Forma Information [Abstract]
Total revenue	$ 730,632	$ 624,283
Net income	$ 181,718	$ 144,605
Earnings Per Share [Abstract]
Basic (In USD per share)	$ 1.97	$ 1.59
Diluted (In USD per share)	$ 1.93	$ 1.55