Net Income per Share of Common Stock (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator for earnings per share:
Net income that is available to common shareholders	$ 66,333	$ 4,963	$ 28,459
Denominator for basic earnings per share:
Weighted average shares outstanding	21,816,935	21,716,288	21,216,780
Denominator for diluted earnings per share:
Effect of stock options and restricted stock units	342,214	467,249	525,393
Adjusted weighted average shares and assumed conversions	22,159,149	22,183,537	21,742,173
Basic earnings per share	$ 3.04	$ 0.23	$ 1.34
Diluted earnings per share	$ 2.99	$ 0.22	$ 1.31
Antidilutive Securities, Excluded From Calculation [Member]
Shares excluded from diluted earnings per share due to:
Inclusion would have been anti-dilutive (excluded from calculation)	105,201	168,557	202,375