Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	9 Months Ended	12 Months Ended	33 Months Ended	42 Months Ended	72 Months Ended	88 Months Ended
	Apr. 27, 2016	Apr. 30, 2016	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2015	Sep. 30, 2016	Dec. 31, 2014	Jun. 30, 2016
Common Equity
Number of shares outstanding (in shares)			175,945,568	175,184,519	175,184,519	175,945,568
Common stock subject to redemption, Value			$ 11,600	$ 6,300	$ 6,300	$ 11,600
Noncontrolling Interests
Percentage of noncontrolling interests based on total shares			3.00%			3.00%
Percentage of noncontrolling interests based on weighted average shares			3.00%			3.00%
Issuance of limited partnership units			$ 11,941	$ 7,282
Partnership unit exchange (in share)			1
Number of limited partnership units related to redemption requests (in shares)			0	0
Affiliated Entity
Noncontrolling Interests
Operating Partnership issued in exchange for certain properties			$ 6,600
Unaffiliated Entity
Noncontrolling Interests
Operating Partnership issued in exchange for certain properties			100
Non- controlling Interests
Noncontrolling Interests
Issuance of limited partnership units		$ 11,900	$ 11,941	$ 7,282
HealthSpring
Noncontrolling Interests
Property interest acquired (percent)	90.00%
Share Redemption Program
Common Equity
Period for written notice								30 days
Maximum redemption percentage of weighted average shares outstanding			5.00%
Shares subject to redemption requests (in shares)			1,159,442			1,159,442
Share Redemption Program | Weighted Average
Common Equity
Share price (in dollars per share)			$ 9.91			$ 9.91
Share Redemption Program | Common Stock
Common Equity
Stock redeemed during period (in shares)						4,768,238
Value of shares redeemed			$ 47,200		17,300	$ 47,200
Private Placement
Common Equity
Proceeds from issuance of private placement			1,400,000				$ 1,300,000
Distribution Reinvestment Plan
Common Equity
Period for written notice								10 days
Common stock issued			$ 149,500	$ 110,200	$ 110,200	$ 149,500