Capital Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Capital Stock [Abstract]
Preferred stock, shares authorized (in shares)		2,000,000
Equity offering	2,875,000
Net proceeds of equity offering	$ 217,600	$ 217,565