Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Supplemental disclosure:
Interest paid	$ 0	$ 0	$ 0	$ 0
Income taxes paid	10,329	6,643	10,847	10,846
Non-cash investing and financing activities:
Non-cash capital expenditures	1,047	(102)	1,312	(173)
Dividends declared	$ 5,834	$ 5,982	$ 5,834	$ 5,982