Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Supplemental non-cash investing and financing activities:
Value of common stock issued in payment of accrued liability	$ 0	$ 188
Exercise of stock options by common stock surrender	0	5,814
Supplemental cash payment information:
Interest paid	983	1,069
Income taxes paid, net of refunds (received, net of payments)	$ 327	$ (9,489)