Subsequent Events (Details) - USD ($)		1 Months Ended	3 Months Ended	4 Months Ended	12 Months Ended
	Apr. 23, 2018	Apr. 30, 2018	Mar. 31, 2018	Apr. 30, 2018	Dec. 31, 2017	Apr. 17, 2018
Subsequent Event [Line Items]
Stock repurchase authorized amount			$ 200,000,000.0
Shares repurchased during period			$ 31,961,000
Number of shares repurchased during period (in shares)			1,304,194		0
Subsequent Event
Subsequent Event [Line Items]
Shares repurchased during period		$ 21,800,000		$ 53,800,000
Number of shares repurchased during period (in shares)		936,541		2,240,735
Subsequent Event | Fund II
Subsequent Event [Line Items]
Capital distribution	$ 15,000,000
Subsequent Event | Fund II | Partnership Interest
Subsequent Event [Line Items]
Capital distribution	$ 4,300,000
Subsequent Event | Disposed of by sale | Sherman Avenue [Member] | Fund II
Subsequent Event [Line Items]
Consideration received						$ 26,000,000