Schedule Of Selected Quarterly Financial Data (Unaudited) (Details) (USD $)	3 Months Ended							12 Months Ended			15 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Selected Quarterly Financial Data [Abstract]
Revenues	$ 26,819,000	$ 24,297,000	$ 21,817,000	$ 24,020,000	$ 21,578,000	$ 21,369,000	$ 21,691,000	$ 96,953,000	$ 87,213,000	$ 82,579,000	$ 22,575,000
Investment and other gains	4,759,000	46,000	35,000	37,000	1,114,000	8,661,000	192,000	4,877,000	10,261,000	272,000	294,000
Income from continuing operations attributable to common stockholders	28,139,000	13,282,000	15,859,000	17,216,000	16,668,000	23,985,000	15,537,000	74,496,000	73,192,000	61,786,000	17,002,000
Discontinued operations	12,966,000	1,068,000	1,068,000	1,133,000	2,140,000	1,132,000	3,556,000				1,112,000
Net income attributable to common stockholders	41,105,000	14,350,000	16,927,000	18,349,000	18,808,000	25,117,000	19,093,000	90,731,000	81,132,000	69,421,000	18,114,000
Basic	27,848,002	27,830,311	27,792,834	27,776,104	27,729,560	27,708,136	27,696,727	27,811,813	27,719,096	27,664,482	27,741,961
Diluted	27,868,245	27,862,582	27,820,831	27,803,222	27,789,725	27,799,616	27,796,109	27,838,720	27,792,592	27,732,959	27,784,915
Basic:
Income from continuing operations attributable to common stockholders	$ 1.01	$ 0.48	$ 0.57	$ 0.62	$ 0.60	$ 0.87	$ 0.56	$ 2.68	$ 2.64	$ 2.23	$ 0.61
Discontinued operations	$ 0.47	$ 0.04	$ 0.04	$ 0.04				$ 0.58	$ 0.29	$ 0.28
Net income attributable to common stockholders	1.48	0.52	0.61	0.66	0.68	0.91	0.69				0.65
Diluted:
Income from continuing operations attributable to common stockholders	$ 1.01	$ 0.48	$ 0.57	$ 0.62	$ 0.60	$ 0.86	$ 0.56	$ 2.68	$ 2.63	$ 2.23	$ 0.61
Discontinued operations	$ 0.47	$ 0.04	$ 0.04	$ 0.04	$ 0.08	$ 0.04	$ 0.13	$ 0.58	$ 0.29	$ 0.27	$ 0.04
Net income attributable to common stockholders	$ 1.48	$ 0.52	$ 0.61	$ 0.66	$ 0.68	$ 0.90	$ 0.69				$ 0.65