Revenue Recognition - Contract Balances (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Receivables, which are included in accounts receivable - trade, net	$ 2,321,000		$ 2,321,000		$ 2,050,000
Contract assets, net, which are included in other current assets	9,481,000		9,481,000		9,264,000
Payables, which are included in other current liabilities	1,373,000		1,373,000		1,082,000
Contract liabilities, which are included in other current liabilities	8,159,000		8,159,000		7,071,000	$ 0
Contract assets, net, which are included in other assets	18,693,000		18,693,000		15,794,000
Contract liabilities, which are included in other liabilities	34,398,000		$ 34,398,000		$ 30,445,000
Commercial leasing contracts, receivable and payable term expectation			12 months
Contract liabilities estimated to be recognized over next twelve months	8,159,000		$ 8,159,000
Revenue recognized on contract liabilities			5,031,000
Revenue recognized relating to performance obligations satisfied or partially satisfied in prior periods	$ 0	$ 0	$ 0	$ 0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation term	2 years		2 years