Background and Basis of Presentation - Summary of Earnings, Weighted Average Common Shares and Potential Common Shares Outstanding (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income for basic and diluted earnings per share	$ 65,922	$ 55,464	$ 99,657	$ 89,026
Denominator:
Weighted average common shares outstanding - basic	192,162	193,092	191,767	193,555
Dilutive effect of equity-based awards	3,024	4,126	3,579	4,618
Weighted average common shares outstanding - diluted	195,186	197,218	195,346	198,173
Earnings per share:
Basic	$ 0.34	$ 0.29	$ 0.52	$ 0.46
Diluted	$ 0.34	$ 0.28	$ 0.51	$ 0.45