Revenue From Contracts With Customer (Schedule of Remaining Performance Obligations) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 6,989
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01 | Revenue expected to be recognized upon customer acceptance
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 4,146
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01 | Revenue expected to be recognized on contracts for installation services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 551
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01 | Revenue expected to be recognized for extended warranty agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 2,292
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 894
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01 | Revenue expected to be recognized upon customer acceptance
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01 | Revenue expected to be recognized on contracts for installation services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01 | Revenue expected to be recognized for extended warranty agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 894
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 409
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-04-01 | Revenue expected to be recognized upon customer acceptance
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-04-01 | Revenue expected to be recognized on contracts for installation services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-04-01 | Revenue expected to be recognized for extended warranty agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 409
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 218
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01 | Revenue expected to be recognized upon customer acceptance
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01 | Revenue expected to be recognized on contracts for installation services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01 | Revenue expected to be recognized for extended warranty agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 218
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 62
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-04-01 | Revenue expected to be recognized upon customer acceptance
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-04-01 | Revenue expected to be recognized on contracts for installation services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-04-01 | Revenue expected to be recognized for extended warranty agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 62
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01 | Revenue expected to be recognized upon customer acceptance
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01 | Revenue expected to be recognized on contracts for installation services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 0
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01 | Revenue expected to be recognized for extended warranty agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 6
Remaining Performance Obligations, Expected Timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 8,579
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) | Revenue expected to be recognized upon customer acceptance
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	4,146
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) | Revenue expected to be recognized on contracts for installation services
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	551
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) | Revenue expected to be recognized for extended warranty agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Performance Obligations	$ 3,882