EPS (Computation of Basic and Diluted Earnings Per Share) (Details) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2019 USD ($) $ / shares	Sep. 30, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Net income | $		$ 15,238	$ 14,488	$ 13,204	$ 14,273	$ 13,977	$ 14,057	$ 12,217	$ 12,820	$ 57,203	$ 53,071	$ 28,476
Dividends and undistributed earnings allocated to participating securities(1) | $	[1]									(120)	(148)	(118)
Net income available to common shareholders | $										$ 57,083	$ 52,923	$ 28,358
Weighted-average common shares outstanding for basic EPS										15,407,289	15,571,387	15,509,665
Dilutive effect of stock-based awards	[2]									45,733	54,916	78,682
Weighted-average common and potential common shares for diluted EPS										15,453,022	15,626,303	15,588,347
Basic EPS | $ / shares		$ 1.00	$ 0.94	$ 0.85	$ 0.91	$ 0.90	$ 0.90	$ 0.78	$ 0.82	$ 3.70	$ 3.40	$ 1.83
Diluted EPS | $ / shares		$ 0.99	$ 0.94	$ 0.85	$ 0.91	$ 0.89	$ 0.90	$ 0.78	$ 0.82	$ 3.69	$ 3.39	$ 1.82
Shares that were not considered in computation of potential common shares for purposes of diluted EPS										0	0	0
Stockholders' Equity Note, Stock Split, Conversion Ratio										1.5

[1] Represents dividends paid and undistributed earnings allocated to nonvested stock-based awards that contain non-forfeitable rights to dividends.

[2] Represents the effect of the assumed exercise of stock options, vesting of restricted shares and restricted stock units, and issuance of LTIP awards that have met the performance criteria, utilizing the treasury stock method.