Organization and Summary of Significant Accounting Policies (Organization and Revenue Recognition) (Details) $ in Thousands			12 Months Ended
	Aug. 22, 2018 USD ($) NotesSeries	Aug. 04, 2017 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2018 USD ($)
Organizations [Line Items]
Total			$ 1,358,430	$ 1,103,743
Number of business days to pay interest		5 days
Maturity term		10 years
Maintenance Reserves			94,522	75,889
Security Deposit Liability			$ 28,047	25,302
Revenue Recognition
Minimum number of days for which lease rent and maintenance reserve payments are past due			30 days
Lease rent receivables past due			$ 4,800
Maintenance reserve receivables past due			5,600
Unbilled revenue associated with outstanding contracts			600
Revenue			87,009	80,189	$ 57,091
Other
Revenue Recognition
Revenue				1,300
Other Assets
Revenue Recognition
Unbilled revenue associated with outstanding contracts						$ 400
Credit facility at a floating rate of interest of LIBOR plus 2.75%, secured by engines
Organizations [Line Items]
Total			491,000
WEST III Series A 2017 term notes payable at a fixed rate of interest of 4.69%, maturing in August 2042, secured by engines
Organizations [Line Items]
Total			$ 274,205	289,295
Fixed rate (as a percent)			4.69%
WEST III Series B 2017 term notes payable at a fixed rate of interest of 6.36%, maturing in August 2042, secured by engines
Organizations [Line Items]
Total			$ 39,212	$ 41,370
Fixed rate (as a percent)			6.36%
WEST IV
Organizations [Line Items]
Number of series notes | NotesSeries	2
Aggregate principal amount	$ 373,400
WEST IV Series A 2018 term notes payable at a fixed rate of interest of 4.75%, maturing in September 2043, secured by engines
Organizations [Line Items]
Aggregate principal amount	$ 326,800
Total			$ 323,075
Fixed rate (as a percent)			4.75%
Notes issues at price of par (as percentage)	99.99853%
Maturity term	8 years
WEST IV Series B 2018 term notes payable at a fixed rate of interest of 5.44%, maturing in September 2043, secured by engines
Organizations [Line Items]
Aggregate principal amount	$ 46,700
Total			$ 46,154
Fixed rate (as a percent)			5.44%
Notes issues at price of par (as percentage)	99.99504%
Maturity term	8 years
WEST III
Organizations [Line Items]
Number of series notes | item		2
WEST III | WEST III Series A 2017 term notes payable at a fixed rate of interest of 4.69%, maturing in August 2042, secured by engines
Organizations [Line Items]
Aggregate principal amount		$ 293,700
Fixed rate (as a percent)			4.69%
WEST III | WEST III Series B 2017 term notes payable at a fixed rate of interest of 6.36%, maturing in August 2042, secured by engines
Organizations [Line Items]
Aggregate principal amount		$ 42,000
Fixed rate (as a percent)			6.36%
WOLF A340 LLC
Organizations [Line Items]
Previously held interest (as a percent)			50.00%
Acquisition of the remaining outstanding shares (as a percent)			100.00%