Summary of Significant Accounting Policies - Related Party Transaction (Details) (USD $)	12 Months Ended						1 Months Ended	12 Months Ended	1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Performance Shares [Member]	Dec. 31, 2011 Performance Shares [Member]	Dec. 31, 2010 Performance Shares [Member]	Jul. 31, 2012 Director [Member]	Jul. 02, 2012 Director [Member]	Jul. 31, 2012 Director [Member] Time-Vested Shares [Member]	Jul. 31, 2012 Director [Member] Performance Shares [Member]	Jul. 31, 2012 Minimum [Member] Director [Member]	Jul. 31, 2012 Maximum [Member] Director [Member]
Related Party Transaction [Line Items]
Consulting agreement, monthly fee							$ 35,000	$ 35,000
Consulting agreement, term											12 months	18 months
Shares granted				184,192	0	2,000			4,828	9,657
Options granted	116,119	210,000	92,000				13,016
Options granted, grant date fair value per share	$ 17.66	$ 11.37	$ 8.05				$ 52.81