Income Per Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income per share:
Shares used to calculate basic income per share	31,485	31,226	31,441	31,203
Dilutive effect of outstanding stock options, performance stock units and restricted stock units	306	372	360	383
Shares used to calculate diluted income per share	31,791	31,598	31,801	31,586
Stock options
Income per share:
Anti-dilutive securities excluded from computation of diluted income per share	8	271	11	282
Performance stock units
Income per share:
Anti-dilutive securities excluded from computation of diluted income per share	0	151	0	84