Earnings per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Numerator for basic and diluted EPS — net income (loss)	$ 11,217	$ (5,912)	$ 28,098	$ (413)
Denominator for basic EPS — weighted average number of shares (shares)	24,870,779	32,280,535.000	27,503,942	32,371,356
Add — dilutive effect of:
Restricted stock units and Cogent earnout shares	1,502,000	0	938,000	0
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)	26,373,107	32,280,535.000	28,441,476	32,371,356
Earnings per share:
Basic (usd per share)	$ 0.45	$ (0.18)	$ 1.02	$ (0.01)
Diluted (usd per share)	$ 0.43	$ (0.18)	$ 0.99	$ (0.01)
Antidilutive securities excluded from EPS (shares)	189,749	2,006,110	696,417	2,006,110
Cogent Partners, LP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Incremental common shares attributable to dilutive effect of contingently issuable shares (shares)	334,048		334,048

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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