Summary of Significant Accounting Policies - Allowance for Credit Losses and Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Management Fees and Other Revenues
Insurance reserve for insurance subsidiaries and other self-insurance programs	$ 81,800	$ 83,500
Allowance for Credit Losses
Balance, beginning of period	22,498	30,094	$ 33,282
Provision for credit losses	11,304	7,319	6,635
Accounts written off, net of recoveries	(10,342)	(14,915)	(9,823)
Balance, end of period	23,460	22,498	$ 30,094
Income Taxes
Provision for federal income taxes for REIT entities	0
Deferred tax liabilities, net	$ 301,700	$ 265,700