Debt - Carrying Amount (Details) $ in Thousands			1 Months Ended	3 Months Ended
	Mar. 31, 2017 USD ($)	Apr. 30, 2016 USD ($)	Apr. 30, 2016 USD ($)	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Mar. 31, 2018 USD ($)
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Gain on extinguishment of debt					$ (735)
Unamortized original issue discount				$ (3,659)		$ (3,766)
Unamortized deferred financing costs				(8,353)		(8,681)
Total unsecured notes and term loans payable, net				1,262,988		1,262,553
Interest rate swaps that were in a liability position				1,000
Credit Risk Related Contingent Features
Derivative liabilities				1,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Remainder of 2020				26,451
2021				246,795
2022				229,483
2023				289,696
2024				446,548
2025				273,947
Thereafter				2,112,508
Long-term Debt				$ 3,625,428
Interest rate swaps
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Number of agreements | segment				2
Scheduled Principal Payments
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Remainder of 2020				$ 26,451
2021				33,329
2022				28,654
2023				24,339
2024				19,634
2025				17,334
Thereafter				39,865
Long-term Debt				189,606
Balloon Payments
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
2021				213,466
2022				200,829
2023				265,357
2024				426,914
2025				256,613
Thereafter				2,072,643
Long-term Debt				3,435,822
Senior Unsecured Notes
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				375,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 1,075,000		1,075,000
Senior Unsecured Notes | Series A issued November 2015
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Stated interest rate (as a percent)				4.95%
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 75,000		75,000
Senior Unsecured Notes | Series B issued November 2015
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Stated interest rate (as a percent)				5.24%
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 100,000		100,000
Senior Unsecured Notes | Series C issued April 2016
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Stated interest rate (as a percent)				4.73%
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 200,000		200,000
Senior Unsecured Notes | Notes Issued March 2018 99.515 Percent Of Par
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Stated interest rate (as a percent)				4.50%
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 350,000		350,000
Senior Unsecured Notes | Notes Issued February 2019 99.260 Percent Of Par
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Stated interest rate (as a percent)				4.625%
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 350,000		350,000
Public notes
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount							$ 350,000	$ 350,000
Coupon rate							99.26%	99.515%
Public notes | Notes Issued March 2018 99.515 Percent Of Par
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Stated interest rate (as a percent)				4.50%
Public notes | Notes Issued February 2019 99.260 Percent Of Par
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Stated interest rate (as a percent)				4.625%
Term Loan Payable
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount	$ 100,000	$ 100,000	$ 100,000
Term of notes			5 years
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 200,000		200,000
Term Loan Payable | One-Month LIBOR
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Debt Instrument interest rate description				one-month LIBOR
Credit spread (as a percent)	1.00%	1.10%
Term Loan Payable | Term Loan Issued March 2017
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Interest rate				1.94%
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 100,000		100,000
Term Loan Payable | Term Loan Issued March 2017 | One-Month LIBOR
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Debt Instrument interest rate description				one-month LIBOR
Credit spread (as a percent)				1.00%
Term Loan Payable | Term Loan issued April 2016
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Interest rate				2.44%
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 100,000		100,000
Term Loan Payable | Term Loan issued April 2016 | One-Month LIBOR
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Debt Instrument interest rate description				one-month LIBOR
Credit spread (as a percent)				1.10%
Non-recourse net-lease mortgage notes:
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Retained non-amortizing notes				$ 155,000
Consolidated special purpose entities
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Aggregate investment amount				3,200,000
Unamortized original issue discount				(450)		(471)
Unamortized deferred financing costs				(29,054)		(30,350)
Total unsecured notes and term loans payable, net				2,320,924		2,328,489
Consolidated special purpose entities | Non-recourse net-lease mortgage notes:
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				2,156,464		2,164,362
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2015-1, Class A-1 Due April 2022
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				95,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 92,665		92,783
Mortgage Loans on Real Estate, Interest Rate				3.75%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2013-1, Class A-2 Due March 2023
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 102,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 89,242		89,775
Mortgage Loans on Real Estate, Interest Rate				4.65%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2013-2, Class A-2 Due July 2023
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 97,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 85,961		86,445
Mortgage Loans on Real Estate, Interest Rate				5.33%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2013-3, Class A-2 Due November 2023
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 100,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 89,283		89,773
Mortgage Loans on Real Estate, Interest Rate				5.21%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 20141, Class A2 Due April 2024
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 140,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 135,917		136,092
Mortgage Loans on Real Estate, Interest Rate				5.00%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2018-1 Class A-1 Due October 2024
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 150,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 145,610		146,384
Mortgage Loans on Real Estate, Interest Rate				3.96%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2018-1 Class A-3 Due October 2024
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 50,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 49,646		49,708
Mortgage Loans on Real Estate, Interest Rate				4.40%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2015-1, Class A-2 Due April 2025
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 270,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 263,363		263,700
Mortgage Loans on Real Estate, Interest Rate				4.17%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2016-1, Class A-1 (2016) Due Oct 2026
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 200,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 187,362		188,347
Mortgage Loans on Real Estate, Interest Rate				3.96%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2019-1, Class A-1 Due Nov 2026 [Member]
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 81,437		81,859
Mortgage Loans on Real Estate, Interest Rate				2.82%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2019-1, Class A-3 Due Nov 2026 [Member]
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 45,923		45,981
Mortgage Loans on Real Estate, Interest Rate				3.32%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2016-1, Class A-2 (2017) Due April 2027
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 135,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 127,792		128,443
Mortgage Loans on Real Estate, Interest Rate				4.32%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2018-1 Class A-2 Due October 2027
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 228,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 221,326		222,504
Mortgage Loans on Real Estate, Interest Rate				4.29%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2018-1 Class A-4 Due October 2027
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 164,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 162,838		163,043
Mortgage Loans on Real Estate, Interest Rate				4.74%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2019-1, Class A-2 Due Nov 2034 [Member]
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 242,326		243,582
Mortgage Loans on Real Estate, Interest Rate				3.65%
Consolidated special purpose entities | Non-recourse net-lease mortgage notes: | Series 2019-1, Class A-4 Due Nov 2034 [Member]
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 136,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 135,773		135,943
Mortgage Loans on Real Estate, Interest Rate				4.49%
Consolidated special purpose entities | Nonrecourse mortgage notes payable:
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Aggregate investment amount				$ 343,200
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				193,964		194,948
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | Series 2019-1, Class A-1 Due Nov 2026 [Member]
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				82,000
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | Series 2019-1, Class A-3 Due Nov 2026 [Member]
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				46,000
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | Series 2019-1, Class A-2 Due Nov 2034 [Member]
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				244,000
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $16,100 note issued February 2014
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				16,100
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 13,865		13,973
Mortgage Loans on Real Estate, Interest Rate				4.83%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $13,000 note issued May 2012
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 13,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 10,635		10,727
Mortgage Loans on Real Estate, Interest Rate				5.195%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $26,000 note issued August 2012
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 26,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 21,425		21,608
Mortgage Loans on Real Estate, Interest Rate				5.05%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $6,400 note issued November 2012
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 6,400
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 5,273		5,319
Mortgage Loans on Real Estate, Interest Rate				4.707%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $11,895 note issued March 2013
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 11,895
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 9,920		10,004
Mortgage Loans on Real Estate, Interest Rate				4.7315%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $17,500 note issued August 2013
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 17,500
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 15,038		15,150
Mortgage Loans on Real Estate, Interest Rate				5.46%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $10,075 note issued March 2014
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 10,075
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 9,142		9,188
Mortgage Loans on Real Estate, Interest Rate				5.10%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $65,000 note issued June 2016
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 65,000
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 61,252		61,531
Mortgage Loans on Real Estate, Interest Rate				4.75%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $41,690 note issued March 2019
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 41,690
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 41,690		41,690
Mortgage Loans on Real Estate, Interest Rate				4.80%
Consolidated special purpose entities | Nonrecourse mortgage notes payable: | $6,944 notes issued March 2013
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Principal amount				$ 6,944
Scheduled maturities, including balloon payments, on the nonrecourse debt obligations
Long-term Debt				$ 5,724		$ 5,758
Mortgage Loans on Real Estate, Interest Rate				4.50%
Minimum
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Maximum number of months				24 months
Minimum | Term Loan Payable | One-Month LIBOR
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Credit spread (as a percent)			0.90%
Maximum
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Maximum number of months				36 months
Maximum | Term Loan Payable | One-Month LIBOR
Summary of nonrecourse debt obligations of consolidated special purpose entity subsidiaries
Credit spread (as a percent)			1.75%