Earnings per Share - The Computations of Basic and Diluted Earnings (Loss) Per Share (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
Operations:
Net income	$ 6,771	$ 6,228	$ 19,712	$ 16,112
Less: Amounts allocated to participating securities (nonvested shares and units)	222	268	653	692
Net income attributable to common shareholders	$ 6,549	$ 5,960	$ 19,059	$ 15,420
Share information:
Basic weighted average common shares	17,154,303	17,334,330	17,315,890	17,286,258
Incremental shares from potential dilutive securities	769	229	759	0
Diluted weighted average common shares	17,155,072	17,334,559	17,316,649	17,286,258
Basic and diluted earnings per share (in usd per share)	$ 0.38	$ 0.34	$ 1.10	$ 0.89