Recent Accounting Standards - Line Items Adjusted in Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	$ 12,699	$ 18,184	$ 19,200	$ 43,694
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			3,483	12,009
Deferred taxes			(6,667)	(5,508)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets			(1,075)	(5,042)
Deposits and other assets			(956)	(1,288)
Accrued compensation and employee benefits			(3,901)	(10,437)
Deferred revenue and advance payments			$ (4,032)	1,140
As Reported | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income		17,924		43,867
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization				9,838
Deferred taxes				(6,214)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets				(3,954)
Deposits and other assets				(1,280)
Accrued compensation and employee benefits				(8,845)
Deferred revenue and advance payments				1,156
Effect of the Adoption | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income		$ 260		(173)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization				2,171
Deferred taxes				706
Changes in operating assets and liabilities:
Prepaid expenses and other current assets				(1,088)
Deposits and other assets				(8)
Accrued compensation and employee benefits				(1,592)
Deferred revenue and advance payments				$ (16)