Income Per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income per share:
Shares used to calculate basic income per share	31,118	31,272	31,069	31,386
Dilutive effect of outstanding stock options, performance stock units and restricted stock units	267	255	271	316
Shares used to calculate diluted income per share	31,385	31,527	31,340	31,702
Stock options
Income per share:
Anti-dilutive securities excluded from computation of diluted income per share	4	7	11	10