Summary of Significant Accounting Policies - Cash And Escrow Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and escrow deposits - restricted, current	$ 37,189	$ 32,864
Cash and escrow deposits - restricted, long term	22,710	28,061
Cash and escrow deposits - restricted, total	59,899	60,925
Real estate tax and property insurance escrows
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and escrow deposits - restricted, current	21,603	19,671
Replacement reserve escrows
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and escrow deposits - restricted, current	10,960	6,970
Resident deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and escrow deposits - restricted, current	678	764
Other
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and escrow deposits - restricted, current	3,948	5,459
Insurance deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and escrow deposits - restricted, long term	12,364	12,941
CCRC escrows
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and escrow deposits - restricted, long term	8,526	13,301
Debt service reserve
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and escrow deposits - restricted, long term	$ 1,820	$ 1,819