Company Information and Significant Accounting Policies Schedule of Error Corrections and Prior Period Adjustments (Details) (USD $)	9 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended			3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended			3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013 As Previously Reported [Member]	Mar. 31, 2012 As Previously Reported [Member]	Jun. 30, 2012 As Previously Reported [Member]	Sep. 30, 2012 As Previously Reported [Member]	Dec. 31, 2012 As Previously Reported [Member]	Dec. 31, 2011 As Previously Reported [Member]	Dec. 31, 2010 As Previously Reported [Member]	Mar. 31, 2013 Adjustment [Member]	Mar. 31, 2012 Adjustment [Member]	Jun. 30, 2012 Adjustment [Member]	Sep. 30, 2012 Adjustment [Member]	Dec. 31, 2012 Adjustment [Member]	Dec. 31, 2011 Adjustment [Member]	Dec. 31, 2010 Adjustment [Member]	Mar. 31, 2013 As Revised [Member]	Mar. 31, 2012 As Revised [Member]	Jun. 30, 2012 As Revised [Member]	Sep. 30, 2012 As Revised [Member]	Dec. 31, 2012 As Revised [Member]	Dec. 31, 2011 As Revised [Member]	Dec. 31, 2010 As Revised [Member]
Forgivable notes receivable, net	$ (5,722,000)	$ (2,853,000)	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ (1,729,000)	$ (475,000)	$ (1,537,000)	$ (2,853,000)	$ (10,898,000)	$ (3,475,000)	$ (1,120,000)	$ (1,729,000)	$ (475,000)	$ (1,537,000)	$ (2,853,000)	$ (10,898,000)	$ (3,475,000)	$ (1,120,000)
Net cash provided (used) by operating activities	105,009,000	118,423,000	1,874,000	4,412,000	37,802,000	121,276,000	161,020,000	134,844,000	144,935,000	(1,729,000)	(475,000)	(1,537,000)	(2,853,000)	(10,898,000)	(3,475,000)	(1,120,000)	145,000	3,937,000	36,265,000	118,423,000	150,122,000	131,369,000	143,815,000
Issuance of mezzanine and other notes receivable	0	(4,236,000)	(1,729,000)	(3,719,000)	(5,820,000)	(7,305,000)	(34,925,000)	(12,766,000)	(11,786,000)	1,729,000	583,000	1,684,000	3,069,000	11,189,000	3,539,000	1,203,000	0	(3,136,000)	(4,136,000)	(4,236,000)	(23,736,000)	(9,227,000)	(10,583,000)
Collections of mezzanine and other notes receivable	224,000	110,000	19,000	151,000	210,000	326,000	3,561,000	4,754,000	5,083,000	0	(108,000)	(147,000)	(216,000)	(291,000)	(64,000)	(83,000)	19,000	43,000	63,000	110,000	3,270,000	4,690,000	5,000,000
Net cash provided (used) in investing activities	$ 28,350,000	$ 16,709,000	$ (13,816,000)	$ (1,496,000)	$ (10,387,000)	$ (19,562,000)	$ (57,999,000)	$ (23,804,000)	$ (32,155,000)	$ 1,729,000	$ 475,000	$ 1,537,000	$ 2,853,000	$ 10,898,000	$ 3,475,000	$ 1,120,000	$ (12,087,000)	$ (1,021,000)	$ (8,850,000)	$ (16,709,000)	$ (47,101,000)	$ (20,329,000)	$ (31,035,000)