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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operations:
Net income	$ 9,532	$ 6,771	$ 22,899	$ 19,712
Income attributable to participating securities	294	222	711	653
Net income attributable to common shareholders and used in EPS calculation (Note 3)	$ 9,238	$ 6,549	$ 22,188	$ 19,059
Share information:
Basic weighted average common shares	16,653,717	17,154,303	16,626,024	17,315,890
Incremental shares from potential dilutive securities	0	769	0	759
Diluted weighted average common shares	16,653,717	17,155,072	16,626,024	17,316,649
Basic and diluted earnings per share (in usd per share)	$ 0.55	$ 0.38	$ 1.33	$ 1.10