Earnings per Share - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Numerator for basic and diluted EPS — net income allocated to common stockholders	$ 23,700	$ 13,100	$ 19,700	$ 4,400	$ 7,900	$ 600	$ 9,300	$ 7,600	$ 60,762	$ 25,598	$ 43,388
Denominator for basic EPS — weighted average number of shares (shares)									32,042,594	31,197,288	30,354,227
Add — dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units (shares)									31,000	3,000	4,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)									32,074,232	31,200,378	30,357,691
Earnings per share:
Basic (usd per share)	$ 0.74	$ 0.41	$ 0.62	$ 0.14	$ 0.25	$ 0.02	$ 0.30	$ 0.25	$ 1.90	$ 0.82	$ 1.43
Diluted (usd per share)	$ 0.74	$ 0.41	$ 0.62	$ 0.14	$ 0.25	$ 0.02	$ 0.30	$ 0.25	$ 1.89	$ 0.82	$ 1.43