Debt - Senior Unsecured Credit Facility (Details)	3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	May 04, 2018 USD ($)
Line of Credit Facility [Line Items]
Percent of unused portion line of credit facility triggering lower commitment fee (as a percent)	50.00%
Net proceeds from future equity issuances (as a percent)	75.00%
Unsecured credit facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	$ 300,000,000
Increase in credit facility	600,000,000
Senior unsecured credit facility	0
Interest and unused credit facility fees	$ 400,000	$ 300,000
Minimum
Line of Credit Facility [Line Items]
Line of credit facility, unused capacity, commitment fee (as a percent)	0.20%
Maximum
Line of Credit Facility [Line Items]
Line of credit facility, unused capacity, commitment fee (as a percent)	0.30%
Line Of Credit Facility Covenant Actual Results
Line of Credit Facility [Line Items]
Maximum leverage ratio (as a percent)	0.282
Minimum fixed charge coverage ratio	4.27
Minimum tangible net worth	$ 2,580,000,000
Secured recourse indebtedness ratio	21.30%
Line Of Credit Facility Covenant
Line of Credit Facility [Line Items]
Maximum leverage ratio (as a percent)	0.60
Minimum fixed charge coverage ratio	1.5
Minimum tangible net worth	$ 1,920,000,000
Secured recourse indebtedness ratio	45.00%
LIBOR | Unsecured credit facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Less than or equal to 35% | Maximum | Unsecured credit facility
Line of Credit Facility [Line Items]
Ratio of net indebtedness to EBITDA	0.35
Less than or equal to 35% | LIBOR | Unsecured credit facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Greater than 35% but less than or equal to 45% | Minimum | Unsecured credit facility
Line of Credit Facility [Line Items]
Ratio of net indebtedness to EBITDA	0.35
Greater than 35% but less than or equal to 45% | Maximum | Unsecured credit facility
Line of Credit Facility [Line Items]
Ratio of net indebtedness to EBITDA	0.45
Greater than 35% but less than or equal to 45% | LIBOR | Unsecured credit facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.65%
Greater than 45% but less than or equal to 50% | Minimum | Unsecured credit facility
Line of Credit Facility [Line Items]
Ratio of net indebtedness to EBITDA	0.45
Greater than 45% but less than or equal to 50% | Maximum | Unsecured credit facility
Line of Credit Facility [Line Items]
Ratio of net indebtedness to EBITDA	0.50
Greater than 45% but less than or equal to 50% | LIBOR | Unsecured credit facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.80%
Greater than 50% but less than or equal to 55% | Minimum | Unsecured credit facility
Line of Credit Facility [Line Items]
Ratio of net indebtedness to EBITDA	0.50
Greater than 50% but less than or equal to 55% | Maximum | Unsecured credit facility
Line of Credit Facility [Line Items]
Ratio of net indebtedness to EBITDA	0.55
Greater than 50% but less than or equal to 55% | LIBOR | Unsecured credit facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Greater than 55% | Minimum | Unsecured credit facility
Line of Credit Facility [Line Items]
Ratio of net indebtedness to EBITDA	0.55
Greater than 55% | LIBOR | Unsecured credit facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.25%
Subsequent Event | Unsecured credit facility
Line of Credit Facility [Line Items]
Senior unsecured credit facility			$ 20,000,000