Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 120,073	$ 118,859	$ 118,021	$ 113,530	$ 110,910	$ 106,243	$ 105,686	$ 100,154	$ 470,483	$ 422,993	$ 396,679
Aerospace and Defense [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,306				4,355				19,405	19,060
Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	21,164				19,537				86,968	74,605
Medical [Member]
Disaggregation of Revenue [Line Items]
Revenues	11,370				10,474				40,663	35,264
Telecommunications & IT [Member]
Disaggregation of Revenue [Line Items]
Revenues	6,504				4,978				23,323	18,813
Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 76,729				$ 71,566				$ 300,124	$ 275,251