Earnings per Share Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator [Line items]
Net income	$ 48,399	$ 52,837	$ 75,418	$ 76,741
Denominators [Line Items]
Weighted average Class A common shares outstanding – Basic	57,187	55,976	57,106	55,902
Weighted average Class B common shares outstanding	793	915	793	958
Dilutive effect of employee stock-based awards	137	252	137	272
Weighted average shares - Diluted	58,117	57,143	58,036	57,132
Earnings per common share [Line Items]
Basic earnings per common share	$ 0.85	$ 0.94	$ 1.32	$ 1.37
Diluted earnings per common share	$ 0.83	$ 0.92	$ 1.30	$ 1.34