Revenue Recognition Contract Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Jan. 01, 2018
Revenue Recognition [Abstract]
Contract with Customer, Liability	$ 239,373	$ 239,373	$ 242,017	$ 247,296
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price	0	0
Contract with Customer, Liability, Revenue Recognized	(2,644)	(7,923)
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 2,643	$ 2,643
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	3 months	3 months
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 10,566	$ 10,566
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 10,568	$ 10,568
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 10,566	$ 10,566
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 10,566	$ 10,566
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 10,566	$ 10,566
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year
Performance Obligations Related To Contract Liabilities [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 183,898	$ 183,898
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year	1 year