Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]		Total
Balance (in shares) at Dec. 31, 2015	14,919
Balance at Dec. 31, 2015	$ 10,616	$ 44,180	$ 231,091	$ 632		$ 286,519
Net income			41,027			41,027
Other comprehensive loss, net of tax				(2,131)		(2,131)
Stock compensation expense		2,473				2,473
Stock issued for stock-based awards, net of withholdings to satisfy employee tax obligations upon award (in shares)	214
Stock issued for stock-based awards, net of withholdings to satisfy employee tax obligations upon award	$ 711	5,217				2,124
Adjustments to Retained Earnings upon Satisfaction of Employee Tax Obligations			(3,804)
3 for 2 stock split (see note 14) (in shares)	7,494
3 for 2 stock split (see note 14)	$ 24,956	(24,956)
Cash dividends declared			(16,140)			(16,140)
Shares repurchased or cancelled (in shares)	(10)
Shares repurchased or cancelled	$ (33)	(232)
Adjustments to Retained Earnings, Shares repurchased or cancelled			265
Balance (in shares) at Dec. 31, 2016	22,617
Balance at Dec. 31, 2016	$ 36,250	26,682	252,439	(1,499)		313,872
Net income			38,043			38,043
Other comprehensive loss, net of tax				(431)		(431)
Stock compensation expense		2,892				2,892
Stock issued for stock-based awards, net of withholdings to satisfy employee tax obligations upon award (in shares)	69
Stock issued for stock-based awards, net of withholdings to satisfy employee tax obligations upon award	$ 231	2,500				(2,605)
Adjustments to Retained Earnings upon Satisfaction of Employee Tax Obligations			(5,336)
Cash dividends declared			(18,127)			(18,127)
Shares repurchased or cancelled (in shares)	(7)
Shares repurchased or cancelled	$ (24)	(150)
Adjustments to Retained Earnings, Shares repurchased or cancelled			174
Balance (in shares) at Dec. 31, 2017	22,679
Balance at Dec. 31, 2017	$ 36,457	31,924	267,193	(1,930)	[1]	333,644
Net income			55,517			55,517
Other comprehensive loss, net of tax				(2,706)		(2,706)
Stock compensation expense		4,027				4,027
Stock issued for stock-based awards, net of withholdings to satisfy employee tax obligations upon award (in shares)	75
Stock issued for stock-based awards, net of withholdings to satisfy employee tax obligations upon award	$ 249	987				(2,158)
Adjustments to Retained Earnings upon Satisfaction of Employee Tax Obligations			(3,394)
Cash dividends declared			(21,824)			(21,824)
Shares repurchased or cancelled (in shares)	(5)
Shares repurchased or cancelled	$ (17)	(141)
Adjustments to Retained Earnings, Shares repurchased or cancelled			158
Reclassification adjustment under Accounting Standards Update 2018-02			506	(506)
Balance (in shares) at Dec. 31, 2018	22,749
Balance at Dec. 31, 2018	$ 36,689	$ 36,797	$ 298,156	$ (5,142)		$ 366,500

[1] December 31, 2017 AOCI component balances reflect a correction of incorrectly reported year-end balances in Note 12 of the 2017 Form 10-K, which were presented as $(2,278), $234, and $(392) for securities available for sale, cash flow hedges, and minimum pension liability, respectively.