Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Allowance for doubtful accounts receivable	$ 274	$ 242
Allowance for doubtful notes receivable	$ 7,627	$ 7,937
Preferred stock, par value (in dollars per shares)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	124,896,765	124,896,765
Common stock, shares outstanding (in shares)	89,449,342	80,565,563
Treasury stock, shares (in shares)	35,447,423	44,331,202
Series A Cumulative Preferred Stock, 1,657,206 shares issued and outstanding at September 30, 2014 and December 31, 2013
Preferred stock, shares issued (in shares)	1,657,206	1,657,206
Preferred stock, shares outstanding (in shares)	1,657,206	1,657,206
Series D Cumulative Preferred Stock, 9,468,706 shares issued and outstanding at September 30, 2014 and December 31, 2013
Preferred stock, shares issued (in shares)	9,468,706	9,468,706
Preferred stock, shares outstanding (in shares)	9,468,706	9,468,706
Series E Cumulative Preferred Stock, 4,630,000 shares issued and outstanding at September 30, 2014 and December 31, 2013
Preferred stock, shares issued (in shares)	4,630,000	4,630,000
Preferred stock, shares outstanding (in shares)	4,630,000	4,630,000