Revenue (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total assets	$ 1,678,587	$ 1,678,587		$ 1,651,983
Retained earnings	103,764	103,764		72,741
Contract balances, deferred revenue	8,300	8,300		3,400
Contract assets				$ 1,000
Contract costs	9,500	9,500	$ 9,300
Amortization expense, deferred costs	700	2,200
Revenue recognized attributable to changes in the estimated transaction price	$ (100)	$ (400)
ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total assets			9,300
Retained earnings			6,900
Deferred tax liabilities			$ 2,400