Income taxes - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2013
Valuation Allowance [Line Items]
Cumulative valuation allowance		$ (5,600,000)
Deferred Tax Assets and Tax Credit Carryforwards, Cumulative		82,500,000
Net Deferred Tax Liabilities	(7,117,000)	(7,094,000)
Deferred tax liability, indefinite-lived intangible assets	7,117,000	7,094,000
Tax credit carryforward		3,900,000
Unrecognized Tax Benefits and Income Tax Penalties and Interest Accrued	72,000	63,000
Unrecognized tax benefits, which if recognized would impact on effective tax rate		40,000
Interest on income tax	20,000
Accrued interest and penalties from unrecognized tax positions	22,000	22,000
Non-recurring tax benefit		1,300,000
Federal
Valuation Allowance [Line Items]
Operating loss carryforwards		$ 130,600,000