Business Segment, Geographic and Major Customer Information (Revenue by Geographic Location) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue by geographic location
Revenue	$ 70,604	$ 64,337	$ 64,079	$ 63,812	$ 63,863	$ 74,048	$ 71,949	$ 60,106	$ 262,832	$ 269,966	$ 319,852
U.S.
Revenue by geographic location
Revenue									210,890	227,117	262,430
Other countries
Revenue by geographic location
Revenue									$ 51,942	$ 42,849	$ 57,422