Income Per Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income per share:
Shares used to calculate basic income per share	31,072	31,485	31,044	31,441
Dilutive effect of outstanding stock options, performance stock units and restricted stock units	263	306	271	360
Shares used to calculate diluted income per share	31,335	31,791	31,315	31,801
Stock options
Income per share:
Anti-dilutive securities excluded from computation of diluted income per share	11	8	11	11