Earnings per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Numerator for basic and diluted EPS — net income allocated to common stockholders	$ 7,900	$ 600	$ 9,300	$ 7,600	$ 15,300	$ 19,800	$ 8,000	$ 300	$ 25,598	$ 43,388	$ 46,682
Denominator for basic EPS — weighted average number of shares (shares)									31,197,288	30,354,227	30,134,430
Add — dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units (shares)									3,000	4,000	27,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)									31,200,378	30,357,691	30,160,669
Earnings per share:
Basic (usd per share)	$ 0.25	$ 0.02	$ 0.30	$ 0.25	$ 0.51	$ 0.66	$ 0.27	$ 0.01	$ 0.82	$ 1.43	$ 1.55
Diluted (usd per share)	$ 0.25	$ 0.02	$ 0.30	$ 0.25	$ 0.51	$ 0.66	$ 0.27	$ 0.01	$ 0.82	$ 1.43	$ 1.55