Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Supplemental disclosure:
Interest paid	$ 0	$ 0	$ 0	$ 0
Income taxes paid	6,643	9,850	10,846	10,533
Non-cash investing and financing activities:
Non-cash capital expenditures	(102)	262	(173)	264
Dividends declared	$ 5,982	$ 4,779	$ 5,982	$ 4,779