Stockholders' Equity (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Restricted stock activity
Restricted shares outstanding, beginning of period	$ 22.87	$ 24.15	$ 42.78
Restricted shares outstanding, beginning of period, shares	734,286	703,856	586,325
Restricted shares granted	$ 40.28	$ 25.41	$ 12.48
Restricted shares granted, shares	499,050	388,650	433,210
Restricted shares canceled	$ 32.29	$ 24.45	$ 41.86
Restricted shares canceled, shares	(49,661)	(46,029)	(51,750)
Restricted shares vested	$ 24.84	$ 28.75	$ 42.92
Restricted shares vested, shares	(348,972)	(312,191)	(263,929)
Restricted shares outstanding, end of period	$ 31.89	$ 22.87	$ 24.15
Restricted shares outstanding, end of period, shares	834,703	734,286	703,856