Notes payable, convertible senior notes and line of credit - Additional Information (Detail)			1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 10, 2016 USD ($)	Jan. 26, 2016 USD ($)	Oct. 31, 2014 USD ($) shares	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($) shares	Oct. 31, 2009 USD ($)
Debt Disclosure [Abstract]
Principal payments on notes in 2016					$ 2,500,000
Principal payments on notes in 2017					1,300,000
Principal payments on notes in 2018					400,000
Principal payments on notes in 2019					98,200,000
Debt Instrument [Line Items]
Capital lease obligations					4,399,000	$ 11,180,000
Notes payable, debt issuance cost					3,300,000
Notes payable, amortization of debt issuance costs						300,000	$ 400,000
Notes payable, interest expense						1,300,000	2,000,000
Impairment charge				$ 35,900,000	35,749,000	0	0
Subsequent Event | Conversion, Class B Common Stock to Common Stock
Debt Instrument [Line Items]
Conversion of Stock, additional cash issued to Class B Common Stock holders		$ 12,000,000
Line of Credit
Debt Instrument [Line Items]
Bank line of credit facility amount					125,000,000
Bank line of credit facility, outstanding					98,000,000
Line of credit, conditional increase in maximum borrowing capacity					$ 50,000,000.0
Fixed charge ratio, minimum					1.25
Leverage ratio, maximum					2.25
Maximum aggregate annual capital expenditures allowed					$ 20,000,000
Annual dividend payments allowed, maximum					$ 25,000,000.0
Line of Credit | Subsequent Event
Debt Instrument [Line Items]
Maximum aggregate annual capital expenditures allowed	$ 25,000,000
Maximum exception to allowed restricted payments for the new share repurchase program	50,000,000.0
Annual dividend payments allowed, maximum	$ 35,000,000.0
Line of Credit | Base Rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate, line of credit					0.50%
Line of Credit | Base Rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate, line of credit					1.00%
Line of Credit | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate, line of credit					1.50%
Line of Credit | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate, line of credit					2.00%
Convertible Notes Payable
Debt Instrument [Line Items]
Convertible senior notes, aggregate principal amount								$ 65,000,000.0
Convertible senior notes, interest rate								6.00%
Convertible senior notes, carrying amount			$ 27,200,000				$ 37,800,000
Convertible senior notes, shares issued during conversion (in shares) | shares			2,111,017				3,094,440
Capital Lease Obligations
Debt Instrument [Line Items]
Capital lease obligations					$ 3,800,000	$ 5,600,000