Equity - Narrative (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended												12 Months Ended			15 Months Ended	12 Months Ended				12 Months Ended	3 Months Ended				12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012 class_of_stock	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Dec. 31, 2012 Officer [Member]	Dec. 31, 2012 Director [Member]	Dec. 31, 2012 Common stock, Class C Non-Voting	Dec. 31, 2012 Common Class A [Member]	Dec. 31, 2010 Series B Preferred Stock [Member]	Mar. 31, 2013 Series A Preferred Stock [Member]	Jan. 17, 2013 Series A Preferred Stock [Member]	Dec. 31, 2012 Series C Preferred Stock	Dec. 31, 2011 Series C Preferred Stock	Dec. 31, 2012 Series C Preferred Stock Issuance To But Excluding January 1 following fifth year [Member]	Dec. 31, 2012 Series C Preferred Stock From January 1 following fifth year of issuance to but excluding January 1 following tenth year [Member]	Dec. 31, 2012 Series C Preferred Stock From January 1 following tenth year of issuance [Member]
Class of Stock [Line Items]
Number of Board of Directors													15	4	7				4
Number of classes of common stock													3
Maximum ownership percentage of common stock by beneficial owner																				33.00%
Common stock dividend, per share, cash paid		$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.40	$ 0.20	$ 0.20
Common stock dividends per common share	$ 0.12	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.05		$ 0.05	$ 0.05				$ 0.40	$ 0.20	$ 0.20	$ 0.05
Loss On Retirement Of Preferred Stock													$ 0	$ 0	$ 5,784						$ 5,800
Preferred stock, Series C, par value																							$ 25	$ 1,000	$ 1,000
Preferred Stock, Liquidation Preference Per Share																							$ 25	$ 1,000
Preferred stock, Series C, shares issued																							2,400,000	57,578	57,578
Preferred stock dividend rate																						5.875%
Preferred stock, Series C, shares outstanding																								57,578	57,578
Preferred Stock, Dividend Rate, Per-Dollar-Amount																										$ 0.050	$ 0.070	$ 0.090
Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award																	P10Y	P7Y