Earnings per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from EPS (shares)	256		35,877
Numerator for basic and diluted EPS — net income (loss) allocated to common stockholders	$ (5,912)	$ 13,110	$ (413)	$ 37,095
Denominator for basic EPS — weighted average number of shares (shares)	32,280,535	31,686,347	32,371,356	31,953,530
Add — dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units (shares)	0	7,000	0	7,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)	32,280,535	31,693,173	32,371,356	31,960,892
Earnings per share:
Basic (usd per share)	$ (0.18)	$ 0.41	$ (0.01)	$ 1.16
Diluted (usd per share)	$ (0.18)	$ 0.41	$ (0.01)	$ 1.16
Cogent Partners, LP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from EPS (shares)			334,048