Commitments and Contingencies (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($)
Purchase Commitment [Line Items]
Single-family properties sales in escrow | property	279	78
Single-family properties sales in escrow, selling price	$ 53.6	$ 13.6
Silver Bay Realty Trust Corp.
Gain (Loss) on Sale of Securities, Net [Abstract]
Gain (loss) on sale of equity investments			$ 3.0
Single Family Properties
Purchase Commitment [Line Items]
Purchase price of commitment to acquire single-family properties	15.1	25.3
Land
Purchase Commitment [Line Items]
Purchase price of commitment to acquire single-family properties	$ 50.8	$ 58.1
Commitment To Acquire Properties
Purchase Commitment [Line Items]
Number of properties | property	47	88