Stockholders' Equity - Components and Voting Power of Outstanding Common Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Common stock, shares outstanding	119,428,910
Percentage	100.00%
Common Class A [Member]
Class of Stock [Line Items]
Common stock, shares outstanding	30,486,858	32,224,421
Percentage	25.50%
Common Class B [Member]
Class of Stock [Line Items]
Common stock, shares outstanding	88,942,052	89,108,569
Percentage	74.50%	73.40%