Income taxes - Schedule of Provision (Benefit) for Income Taxes Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 178	$ (2,600)	$ 1,206
State	3,586	2,941	1,428
Foreign	945	817	421
Total current tax expense	4,709	1,158	3,055
Deferred:
Federal	22,757	365,470	11,633
State	946	6,857	3,755
Foreign	230	95	218
Total deferred tax expense	23,933	372,422	15,606
Provision for income taxes	$ 28,642	$ 373,580	$ 18,661