Earnings per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Numerator for basic and diluted EPS — net income	$ 10,513	$ 6,245	$ 16,881	$ 5,499
Denominator for basic EPS — weighted average number of shares (shares)	26,992,652	31,933,830	28,545,545	32,151,409
Add — dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units (shares)	929,000	44,000	679,000	100,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)	27,921,821	31,977,479	29,224,878	32,251,500
Earnings per share:
Basic (usd per share)	$ 0.39	$ 0.20	$ 0.59	$ 0.17
Diluted (usd per share)	$ 0.38	$ 0.20	$ 0.58	$ 0.17
Antidilutive securities excluded from EPS (shares)	563,778	1,436,970	619,235	1,386,443
Cogent Partners, LP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Incremental common shares excluded from dilutive effect of contingently issuable shares (shares)			334,048

Incremental Common Shares Excluded From Dilutive Effect of Contingently Issuable Shares

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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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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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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