Stockholders' Equity (Details 2) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended			12 Months Ended
	Jan. 31, 2011	Dec. 31, 2010	Jan. 05, 2004	Dec. 31, 2012 Nonvested restricted stock awards	Dec. 31, 2011 Nonvested restricted stock awards	Dec. 31, 2010 Nonvested restricted stock awards	Dec. 31, 2012 Restricted stock units	Dec. 31, 2011 Restricted stock units	Dec. 31, 2010 Restricted stock units
Nonvested restricted stock awards and units
Outstanding, beginning of period (in shares)				18,748	22,309	28,910	206,338	190,488	184,454
Awarded (in shares)				23,672	18,748	22,309	131,913	115,003	101,812
Vested (in shares)				(18,748)	(22,309)	(28,910)	(99,976)	(90,853)	(84,615)
Forfeited (in shares)							(35,585)	(8,300)	(11,163)
Outstanding, ending of period (in shares)				23,672	18,748	22,309	202,690	206,338	190,488
Weighted average exercise price of nonvested restricted stock award and units
Outstanding, beginning of period (in dollars per share)				$ 52.11	$ 39.23	$ 30.27	$ 44.63	$ 38.43	$ 34.99
Awarded (in dollars per share)				$ 42.25	$ 52.11	$ 39.23	$ 47.48	$ 49.14	$ 42.75
Vested (in dollars per share)				$ 52.11	$ 39.23	$ 30.27	$ 41.81	$ 37.5	$ 36.2
Forfeited (in dollars per share)							$ 47.43	$ 42.94	$ 37.97
Outstanding, ending of period (in dollars per share)				$ 42.25	$ 52.11	$ 39.23	$ 47.38	$ 44.63	$ 38.43
Unrecognized compensation expense				$ 0.4			$ 3.7
Unrecognized compensation expense, period of recognition				4 months 13 days			1 year 10 months 24 days
Warrants issued to purchase common stock (in shares)			570,825
Fair value per warrant			$ 9.44
Purchase price of common stock (in dollars per share)			$ 30.46
Warrants outstanding at the end of the period (in shares)		44,561
Exercise of stock warrants (in shares)	31,362
Warrants forfeited (in shares)	13,199