Segment Information - Percent of sales revenue by country (Details) - Sales	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
United States of America
Segment Reporting Information [Line Items]
Percentage of sales revenue	97.30%	95.30%	96.80%	96.30%
Mexico
Segment Reporting Information [Line Items]
Percentage of sales revenue	1.20%	3.20%	2.20%	2.70%
Canada
Segment Reporting Information [Line Items]
Percentage of sales revenue	1.30%	1.40%	1.00%	0.90%
All Other Countries (none greater than 0.07%)
Segment Reporting Information [Line Items]
Percentage of sales revenue	0.20%	0.10%	0.00%	0.10%