Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Stock Repurchased and Retired During Period, Shares	121,987
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 174,700
Stock Repurchased and Retired During Period, Value	17,300
Debt and Capital Lease Obligations	45,000	$ 95,000
Stock Repurchase Program, Authorized Amount	250,000
Long-term Debt, Fair Value	$ 46,400	$ 97,100