Earnings Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Apr. 01, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income allocated to common stockholders		$ 9,419	$ 8,054	$ 17,022	$ 8,292
Denominator for basic EPS — weighted average number of shares (shares)		30,934,832	29,954,291	30,707,895	30,218,513
Add — dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units (shares)		91,000	7,000	79,000	36,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)		31,026,098	29,961,023	30,786,714	30,254,549
Earnings per share:
Basic (usd per share)		$ 0.30	$ 0.27	$ 0.55	$ 0.27
Diluted (usd per share)		$ 0.30	$ 0.27	$ 0.55	$ 0.27
Cogent Partners, LP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from EPS (shares)	334,048