Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 24,236	$ 10,987	$ 12,398	$ 12,227	$ 12,591	$ 6,210	$ 12,722	$ 12,501	$ 59,848	$ 44,024	$ 16,736
Weighted average number of shares outstanding- basic (shares)									38,636,152	40,605,464	43,172,528
Effect of dilutive securities:
Total effect of dilutive securities (shares)									138,811	56,840	45,796
Weighted average number of shares outstanding - diluted (shares)									38,774,963	40,662,304	43,218,324
Basic earnings per share (usd per share)	$ 0.64	$ 0.29	$ 0.32	$ 0.31	$ 0.32	$ 0.15	$ 0.31	$ 0.30	$ 1.55	$ 1.08	$ 0.39
Diluted earnings per share (usd per share)	$ 0.64	$ 0.29	$ 0.32	$ 0.31	$ 0.31	$ 0.15	$ 0.31	$ 0.30	$ 1.54	$ 1.08	$ 0.39
Restricted stock awards
Effect of dilutive securities:
Effect of dilutive securities (shares)									7,827	9,018	12,081
Restricted stock units
Effect of dilutive securities:
Effect of dilutive securities (shares)									61,099	31,200	7,000
Performance restricted stock units
Effect of dilutive securities:
Effect of dilutive securities (shares)									47,122	3,557	3,188
Stock options
Effect of dilutive securities:
Effect of dilutive securities (shares)									22,763	13,065	23,527