Stock-Based Compensation (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Share-based Compensation [Abstract]
Number of units deliverable (in shares) | shares	2,600,000
Share conversion ratio	0.7189
Stock-based compensation expense	$ 16,212	$ 10,986	$ 9,205
Immediate expense stock-based compensation	1,436
Tax benefit related to converted shares	1,439	607	609
Unrecognized compensation cost	$ 9,904
Weighted average recognition period (in years)	2 years 10 months 6 days
Additional income tax expense	$ 384
Units/Shares Withheld for Taxes	$ (2,156)	$ 0	$ 0