Summary of significant accounting policies - Long term incentive restricted stock agreements assumptions and vesting requirements (Details)				1 Months Ended	3 Months Ended					12 Months Ended
	Aug. 15, 2014 USD ($) item $ / shares shares	Jun. 27, 2014 USD ($) item $ / shares shares	Jul. 26, 2011 USD ($) item $ / shares shares	Feb. 28, 2014 $ / shares shares	Jun. 30, 2016 USD ($) shares	Mar. 31, 2016 USD ($)	Sep. 30, 2015 USD ($) item $ / shares shares	Sep. 30, 2014 USD ($) shares	Jun. 30, 2014 USD ($) shares	Dec. 31, 2016 shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 shares	Jun. 26, 2011 USD ($)
Restricted Stock With Market Conditions Tranche4 [Member] | Minimum
Valuation assumptions used for estimated fair value on grant date
Risk-free interest rate, low end of the range (as a percent)											0.88%
Restricted Stock With Market Conditions Tranche4 [Member] | Maximum
Valuation assumptions used for estimated fair value on grant date
Expected volatility, high end of the range (as a percent)											31.36%
Restricted Stock With Market Conditions [Member] | Minimum
Valuation assumptions used for estimated fair value on grant date
Expected life											10 months 6 days
Expected volatility, low end of the range (as a percent)											29.97%
Restricted Stock With Market Conditions [Member] | Maximum
Valuation assumptions used for estimated fair value on grant date
Expected life											2 years 8 months 27 days
Risk-free interest rate, high end of the range (as a percent)											0.99%
Restricted Stock With Performance Conditions [Member]
Valuation assumptions used for estimated fair value on grant date
Expected life											1 year 10 months 28 days
Expected volatility (percentage)											29.97%
Risk-free interest rate (percentage)											0.63%
Restricted stock
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)										59,260
Number of shares outstanding										606,596	1,224,737
Restricted stock awards vested (in shares)										677,401
Restricted stock | Awarded third quarter 2015, expires May 1, 2018
Long-term incentive restricted stock agreements assumptions and vesting requirements
Number of tranches | item							4
Restricted stock | Directors
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)								205,830	205,830		152,835
Fair value of awards granted | $								$ 500,000	$ 500,000		$ 300,000
Requisite service period								12 months			12 months
Restricted stock | Employees
Long-term incentive restricted stock agreements assumptions and vesting requirements
Requisite service period											36 years
Restricted stock | Officers | Awarded third quarter 2015, expires May 1, 2018
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)							300,000
Restricted stock | Officers | Awarded third quarter 2015 expires December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Number of tranches | item							2
Restricted stock | Philip Beck | Board Of Directors Chairman [Member]
Long-term incentive restricted stock agreements assumptions and vesting requirements
Percentage of shares repurchased upon exercise of the repurchase option (as a percent)				35.00%
Number of shares repurchased upon exercise of the repurchase option (in shares)				320,250
Repurchase option price (in dollars per share) | $ / shares				$ 1.00
Restricted stock | Restricted Stock With Performance And Market Conditions [Member] | Philip Beck | Board Of Directors Chairman [Member]
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)			915,000
Number of separate tranches in which stock-based award will vest | item			4
Restricted stock | Restricted Stock With Market Conditions [Member]
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair value | $			$ 3,640
Restricted stock | Restricted Stock With Market Conditions [Member] | 2012 Equity Incentive Plan
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)	250,000	325,000
Fair value | $	$ 1,023	$ 5,735
Valuation assumptions used for estimated fair value on grant date
Forfeited (in shares)											450,000	125,000
Restricted stock | Restricted Stock With Market Conditions [Member] | Minimum | 2012 Equity Incentive Plan
Valuation assumptions used for estimated fair value on grant date
Closing price of common stock as reported on NASDAQ (in dollars per share) | $ / shares	$ 6.00	$ 6.00
Number of consecutive trading days during which the closing price of the entity's common stock on the NASDAQ stock market must exceed the specified price in order for the award to vest | item	30	30
Minimum per share consideration for change in control for shares to vest (in dollars per share) | $ / shares	$ 6.00	$ 6.00
Fair market value of stock immediately following change of control transaction, upon achievement of which share will be vested (in dollars per share) | $ / shares		$ 6.00
Restricted stock | Restricted Stock With Market Conditions [Member] | Restricted Stock With Market Conditions Tranche4 [Member]
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)			61,100
Fair value | $			$ 3,640
Number of consecutive trading days during which the fair market value of the entity's common stock must exceed the specified price in order for the award to vest | item			75
Restricted stock | Restricted Stock With Market Conditions [Member] | Restricted Stock With Market Conditions Tranche4 [Member] | Minimum
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair market value of stock upon achievement of which share will be vested (in dollars per share) | $ / shares			$ 12.00
Restricted stock | Restricted Stock With Performance Conditions [Member]
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair value | $			$ 300,000
Restricted stock | Restricted Stock With Performance Conditions [Member] | Restricted Stock With Performance Conditions Tranche One [Member]
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)												198,250
Number of shares outstanding												396,500
Restricted stock | Restricted Stock With Performance Conditions [Member] | Restricted Stock With Performance Conditions Tranche Two [Member]
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)			30,550
Fair value | $													$ 19,552
Restricted stock | Restricted Stock With Performance Conditions [Member] | Restricted Stock With Performance Conditions Tranche Two [Member] | Minimum
Long-term incentive restricted stock agreements assumptions and vesting requirements
Adjusted EBITDA per fully diluted share when upon achievement shares will vest (in dollars per share) | $ / shares			$ 0.64
Restricted stock | Restricted Stock With Performance Conditions [Member] | Restricted Stock With Performance Conditions Tranche Three [Member]
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)			304,850
Fair value | $			$ 216,444
Restricted stock | Restricted Stock With Performance Conditions [Member] | Restricted Stock With Performance Conditions Tranche Three [Member] | Minimum
Long-term incentive restricted stock agreements assumptions and vesting requirements
Adjusted EBITDA per fully diluted share when upon achievement shares will vest (in dollars per share) | $ / shares			$ 0.71
Restricted stock | Tranches one, two and three | Officers | Awarded third quarter 2015, expires May 1, 2018
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)							75,000
Fair value of awards granted | $							$ 100,000
Number of tranches | item							3
Restricted stock | Tranche one | Officers | Awarded third quarter 2015, expires May 1, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair value of awards granted | $							$ 100,000
Restricted stock | Tranche two | Officers | Awarded third quarter 2015, expires May 1, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair value of awards granted | $							$ 100,000
Restricted stock | Tranche four | Officers | Awarded third quarter 2015 expires December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)							225,000
Restricted stock | Tranche three | Officers | Awarded third quarter 2015, expires May 1, 2017 and December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Stock granted (in shares)							300,000
Restricted stock awards vested (in shares)					225,000
Number of tranches | item							3
Market condition | Tranches one, two and three | Officers | Awarded third quarter 2015, expires May 1, 2018
Long-term incentive restricted stock agreements assumptions and vesting requirements
Number of consecutive trading days							7 years
Number of trading days | item							10
Period of consecutive days for stock price							35 years
Market condition | Tranche four | Officers | Awarded third quarter 2015, expires May 1, 2018
Long-term incentive restricted stock agreements assumptions and vesting requirements
Share Price For Market Condition | $ / shares							$ 4.00
Market condition | Tranche four | Officers | Awarded third quarter 2015 expires December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair value of awards granted | $							$ 300,000
Restricted stock awards expensed | $					$ 100,000	$ 200,000
Share Price For Market Condition | $ / shares							$ 3.50
Number of consecutive trading days							7 years
Number of trading days | item							10
Period of consecutive days for stock price							35 years
Market condition | Tranche three | Officers | Awarded third quarter 2015 expires December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair value of awards granted | $							$ 300,000
Market condition | Tranche three | Officers | Awarded third quarter 2015, expires May 1, 2017 and December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Restricted stock awards expensed | $					$ 100,000	$ 300,000
Performance shares | Tranche four | Officers | Awarded third quarter 2015 expires December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair value of awards granted | $							600,000
Performance shares | Tranche four | Minimum | Officers | Awarded third quarter 2015 expires December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Threshold for Performance Condition | $							18,000,000
Performance shares | Tranche three | Officers | Awarded third quarter 2015 expires December 31, 2017
Long-term incentive restricted stock agreements assumptions and vesting requirements
Fair value of awards granted | $							$ 600,000