Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Significant Accounting Policies [Line Items]
Maximum maturity period for classification of investments as cash equivalents	3 months
Investments other-than-temporary losses	$ 0	$ 0	$ 0
Allowance for doubtful accounts	178,000	82,000	100,000
Provision for bad debts	400,000	200,000	200,000
Write-offs and other charges against the allowance for doubtful accounts	100,000	100,000	$ 100,000
Deferred tax assets, net	1,737,000	8,562,000
Other comprehensive income	(10,226,000)	(12,228,000)
Prepaid expenses and other assets	$ 18,717,000	$ 11,618,000
Restatement Adjustment [Member]
Significant Accounting Policies [Line Items]
Deferred tax assets, net				$ 3,100,000
Other comprehensive income				2,100,000
Prepaid expenses and other assets				$ 1,000,000
Maximum [Member]
Significant Accounting Policies [Line Items]
Contractual maturities accounts receivable	1 year
Estimated useful life of fixed assets	7 years
Maximum [Member] | Business Combinations [Member]
Significant Accounting Policies [Line Items]
Estimated life of intangible assets	15 years
Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of fixed assets	3 years
Minimum [Member] | Business Combinations [Member]
Significant Accounting Policies [Line Items]
Estimated life of intangible assets	3 years
Minimum [Member] | Internally Developed Software [Member]
Significant Accounting Policies [Line Items]
Estimated life of intangible assets	3 years