Earnings per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Numerator for basic and diluted EPS — net income allocated to common stockholders	$ 684	$ 19,873	$ 17,706	$ 28,165
Denominator for basic EPS — weighted average number of shares (shares)	31,196,845	30,046,450	30,971,658	30,326,050
Add — dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units (shares)	19,000	2,000	52,000	13,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)	31,215,999	30,048,128	31,023,713	30,338,516
Earnings per share:
Basic (usd per share)	$ 0.02	$ 0.66	$ 0.57	$ 0.93
Diluted (usd per share)	$ 0.02	$ 0.66	$ 0.57	$ 0.93
Cogent Partners, LP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from EPS (shares)			334,048