Capital Stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Capital Stock [Abstract]
Maximum amount receivable from sale of securities under shelf registration	$ 250,000,000
Maximum limit of shares sold by stockholder's (in shares)	2,500,000
Issuance of common stock (in shares)	2,757,170
Share price (in dollars per share)	$ 19.85
Proceeds from issuance of common stock	$ 51,543,000	$ 0	$ 22,353,000