Adoption of Accounting Standards Codification 606 - Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income	$ 673	$ 4,171	$ 1,591	$ 2,600	$ 9,484	$ 4,655	$ 3,823	$ 2,115	$ 9,035	$ 20,077	$ 25,261
Other comprehensive income (loss), net of tax									78	(38)	(476)
Adoption of ASC 606 adjustment												$ 8,665
Adoption of ASU 2018-02 adjustment									(26)
Stock options exercised									1,822	4,336	2,122
Stock repurchased related to the exercise of stock options									(6,345)	(6,904)	(3,465)
Stock awards vested									2,973	0	0
Stock-based compensation									5,040	$ 6,009	$ 3,007
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income									(4,660)
Other comprehensive income (loss), net of tax									0
Adoption of ASC 606 adjustment												(8,665)
Adoption of ASU 2018-02 adjustment									0
Stock options exercised									0
Stock repurchased related to the exercise of stock options									0
Stock awards vested									0
Stock-based compensation									0
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income									4,375
Other comprehensive income (loss), net of tax									78
Adoption of ASC 606 adjustment												$ 0
Adoption of ASU 2018-02 adjustment									(26)
Stock options exercised									1,822
Stock repurchased related to the exercise of stock options									(6,345)
Stock awards vested									2,973
Stock-based compensation									$ 5,040