Equity Based Compensation Plans, Restricted stock activity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Series Z Incentive Units [Member]	Dec. 31, 2011 Series Z Incentive Units [Member]	Dec. 31, 2010 Series Z Incentive Units [Member]	Dec. 31, 2013 Long Term Incentive Plans - Z Units and 2014 LTIP Units [Member]	Dec. 31, 2012 Long Term Incentive Plans - Z Units and 2014 LTIP Units [Member]	Dec. 31, 2011 Long Term Incentive Plans - Z Units and 2014 LTIP Units [Member]
Shares [Roll forward]
Unvested at beginning of year (in shares)	24,922	35,219	44,877				140,043	170,019	171,902
Granted (in shares)	1,556	1,614	1,540	50,500	46,500	108,000	50,500	0	46,500
Vested (in shares)	(7,211)	(8,641)	(9,532)				(35,919)	(28,163)	(44,520)
Converted (in shares)							0	0	0
Forfeited and canceled (in shares)	(3,091)	(3,270)	(1,666)				(5,243)	(1,813)	(3,863)
Unvested at end of year (in shares)	16,176	24,922	35,219				149,381	140,043	170,019
Weighted-average grant price [Abstract]
Unvested at beginning of year (in dollars per share)	$ 104.52	$ 98.57	$ 102.46				$ 58.44	$ 58.17	$ 54.15
Granted (in dollars per share)	$ 158.75	$ 149.68	$ 134.44
Vested (in dollars per share)	$ 109.86	$ 106.69	$ 104.91
Forfeited and canceled (in dollars per share)	$ 100.84	$ 102.00	$ 94.35
Unvested at end of year (in dollars per share)	$ 108.06	$ 104.52	$ 98.57				$ 63.53	$ 58.44	$ 58.17
Incentive units vested [Roll Forward]
Vested, beginning balance (in shares)							190,704	179,082	326,280
Vested, units granted (in shares)							0	0	0
Vested, units vested (in shares)							35,919	28,163	44,520
Converted (in shares)							(108,433)	(16,541)	(191,718)
Cancelled (in shares)							0	0	0
Vested, ending balance (in shares)							118,190	190,704	179,082
Aggregate intrinsic value, unvested, beginning balance							$ 20,800	$ 23,719	$ 19,463
Aggregate intrinsic value, unvested, ending balance							$ 21,438	$ 20,800	$ 23,719
Total outstanding incentive units [Abstract]
Total outstanding units, beginning balance (in shares)							330,747	349,101	498,182
Total outstanding units, granted (in shares)							50,500	0	46,500
Total outstanding units, vested (in shares)							0	0	0
Total outstanding units, converted (in shares)							(108,433)	(16,541)	(191,718)
Total outstanding units, cancelled (in shares)							(5,243)	(1,813)	(3,863)
Total outstanding units, ending balance (in shares)							267,571	330,747	349,101
Weighted-average remaining contractual life, beginning balance							11 years 3 months 18 days	12 years 3 months 18 days	11 years 2 months 12 days
Weighted-average remaining contractual life, ending balance							9 years 3 months 18 days	11 years 3 months 18 days	12 years 3 months 18 days