Other Investments Other Investments (Amended Management Agreement) (Details)		12 Months Ended
	Jan. 02, 2019 USD ($) multiple	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Additional cash investment in equity method investment		$ 94,578,000	$ 224,219,000	$ 58,197,000
Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management agreement, share lock up period, subject to certain restrictions	2 years
Management agreement, termination fee as multiple of prior year management fee | multiple	3
Management agreement, equity raised since inception metric related to renewal and termination	$ 820,000,000
Real Estate Investment | Safety, Income and Growth, Inc. | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Additional cash investment in equity method investment	$ 250,000,000
Fee percent of SAFE Equity up to $1.5 billion | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee as percent of equity	1.00%
Fee percent of SAFE Equity up to $1.5 billion | Maximum | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount	$ 1,500,000,000.0
Fee percent of SAFE Equity between $1.5 billion and $3.0 billion | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee as percent of equity	1.25%
Fee percent of SAFE Equity between $1.5 billion and $3.0 billion | Minimum | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount	$ 1,500,000,000.0
Fee percent of SAFE Equity between $1.5 billion and $3.0 billion | Maximum | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount	$ 3,000,000,000.0
Fee percent of SAFE Equity between $3.0 billion and $5.0 billion | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee as percent of equity	1.375%
Fee percent of SAFE Equity between $3.0 billion and $5.0 billion | Minimum | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount	$ 3,000,000,000.0
Fee percent of SAFE Equity between $3.0 billion and $5.0 billion | Maximum | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount	$ 5,000,000,000.0
Fee percent of SAFE Equity over $5.0 billion | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee as percent of equity	1.50%
Fee percent of SAFE Equity over $5.0 billion | Minimum | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount	$ 5,000,000,000.0