Earnings per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Apr. 01, 2015	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Numerator for basic and diluted EPS — net income (loss)		$ (12,697)	$ 10,513	$ (28,083)	$ 16,881
Denominator for basic EPS — weighted average number of shares (shares)		23,925,310	26,992,652	24,231,448	28,545,545
Add — dilutive effect of:
Restricted stock units		0	929,000	0	679,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)		23,925,310	27,921,821	24,231,448	29,224,878
Earnings per share:
Basic (usd per share)		$ (0.53)	$ 0.39	$ (1.16)	$ 0.59
Diluted (usd per share)		$ (0.53)	$ 0.38	$ (1.16)	$ 0.58
Antidilutive securities excluded from EPS (shares)			563,778		619,235
Restricted Stock Units
Earnings per share:
Antidilutive securities excluded from EPS (shares)				3,526,114
Restricted Stock Units
Add — dilutive effect of:
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)		190,930		407,823
Cogent Partners, LP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conditional consideration (shares)	334,048
Earnings per share:
Incremental common shares attributable to dilutive effect of contingently issuable shares (shares)				334,048