Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental non-cash investing and financing activities:
Value of common stock issued in acquisitions	$ 0	$ 3,268	$ 1,014
Value of common stock issued in payment of accrued liability	188	0	0
Exercise of stock options by common stock surrender	5,863	50	1,332
Supplemental cash payment information:
Interest paid	1,851	2,024	1,398
Income taxes (received, net of payments) paid, net of refunds	$ (10,195)	$ 333	$ 1,547