Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended			6 Months Ended	12 Months Ended
	Aug. 08, 2019	Jul. 31, 2019	Dec. 31, 2017	Jun. 30, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Shares repurchased during period (in shares)				0.7	3.3
Value of shares repurchased during period			$ 8,000	$ 5,200	$ 25,900
Weighted average price of shares repurchased (in dollars per share)				$ 7.10	$ 7.91
Share repurchase program, unfulfilled requests (in shares)				12.0
Share repurchase program, unfulfilled requests				$ 85,000
Stock repurchase program, unfilled requests, value per share (in dollars per share)				$ 7.10
Long-term debt				$ 1,466,482
Real estate debt investments, net				$ 56,287	$ 58,600
Subsequent event
Subsequent Event [Line Items]
Shares repurchased during period (in shares)	0.3
Value of shares repurchased during period	$ 2,200
Weighted average price of shares repurchased (in dollars per share)	$ 7.10
Rochester | Subsequent event
Subsequent Event [Line Items]
Long-term debt		$ 12,400
Real estate debt investments, net		$ 12,800
LIBOR | Rochester | Subsequent event
Subsequent Event [Line Items]
Interest rate (percentage)		2.90%