Earnings per share - Additional Information (Detail) - shares	2 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015	Aug. 11, 2015	Aug. 06, 2015
Restricted Stock Units [Member]
Earnings Per Share Diluted [Line Items]
Anti-dilutive securities excluded from the calculation of earnings per share	8,160
Stock Options [Member]
Earnings Per Share Diluted [Line Items]
Anti-dilutive securities excluded from the calculation of earnings per share	116,690	250,141	230,633
Class A Common Stock [Member]
Earnings Per Share Diluted [Line Items]
Common stock, shares outstanding		49,914,000	49,914,000	36,598,000	36,597,985	0
Class B Common Stock [Member]
Earnings Per Share Diluted [Line Items]
Common stock, shares outstanding		48,665,000	48,665,000	62,112,000		0
Class B Common Stock [Member] | Continuing LLC Owners Exchange Agreement
Earnings Per Share Diluted [Line Items]
Anti-dilutive securities excluded from the calculation of earnings per share		53,898,536	59,218,127