Stockholders' Equity (Details) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended	0 Months Ended	12 Months Ended
	Jan. 30, 2010	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	May 31, 2012 Minimum Adage	Sep. 17, 2009 Series A Junior Participating Preferred Stock item	Dec. 31, 2012 Series A Junior Participating Preferred Stock item	Dec. 31, 2012 Series A Junior Participating Preferred Stock Minimum
Preferred Stock
Number of rights for each outstanding share of common stock						1
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01	$ 0.01		$ 0.01
Number of preferred share purchase rights for each outstanding share of the entity's common stock							0.001
Number of days following the acquisition of twenty percent or more of the common stock by person or group whose rights are exercisable							10 days
Percentage of common stock to be acquired by a person or group for rights to be exercisable					25.00%			20.00%
Number of business days following a tender offer or similar transaction resulting in the acquisition of twenty percent of common stock by a person or group whose rights are exercisable							10 days
Percentage of common stock to be acquired in a tender offer or a similar transaction by a person or group for rights to be exercisable							20.00%
Period during which each holder of a right, other than the acquiring person will be entitled to purchase shares of common stock							60 days
Number of multiples of the exercise price that the right holder has the right to receive in value of the entity's common stock							2
Percentage of common stock to be acquired by an acquiring person for exchange of rights								50.00%
Exchange ratio for conversion of right into common stock by the board, if the acquiring person acquires fifty percent or more of the entity's common stock							1
Number of multiples of the exercise price that the right holder has the right to receive in value of the acquiring the company's common stock under the merger or other business combination transaction							2
Common Stock Transactions
Number of shares sold in an underwritten public offering	3,600,000
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01	$ 0.01		$ 0.01
Selling price per share in an underwritten public offering (in dollars per share)	$ 48.25
Gross proceeds from the sale of common stock	$ 173,700,000
Net proceeds from sale of common stock after deducting fees, commissions and other expenses related to offering	$ 165,600,000	$ 165,559,000