CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2015	$ 224	$ 141,626	$ 64,829	$ (6,183)	$ 200,496
Balance (in shares) at Dec. 31, 2015	22,387,797
Increase (Decrease) in Stockholders' Equity
Net income			39,009		39,009
Dividends paid			(21,451)		(21,451)
Adjustment for pension and postretirement benefit liability, net of tax of ($558) in 2018, ($140) in 2017 and $147 in 2016				(231)	(231)
Adjustment for interest rate swap, net of tax of ($64) in 2018, $88 in 2017 and $225 in 2016				(258)	(258)
Stock based compensation	$ 1	2,897			2,898
Stock based compensation (in shares)	113,843
Balance at Dec. 31, 2016	$ 225	144,523	82,387	(6,672)	220,463
Balance (in shares) at Dec. 31, 2016	22,501,640
Increase (Decrease) in Stockholders' Equity
Net income			55,324		55,324
Dividends paid			(21,974)		(21,974)
Prior period adjustment		187			187
Adjustment for pension and postretirement benefit liability, net of tax of ($558) in 2018, ($140) in 2017 and $147 in 2016				233	233
Adjustment for interest rate swap, net of tax of ($64) in 2018, $88 in 2017 and $225 in 2016				(133)	(133)
Shares withheld on restricted stock vesting		(923)			(923)
Stock based compensation	$ 1	3,500			3,501
Stock based compensation (in shares)	89,257
Balance at Dec. 31, 2017	$ 226	147,287	115,737	(6,572)	256,678
Balance (in shares) at Dec. 31, 2017	22,590,897
Increase (Decrease) in Stockholders' Equity
Net income			43,905		43,905
Dividends paid			(24,383)		(24,383)
Adjustment for pension and postretirement benefit liability, net of tax of ($558) in 2018, ($140) in 2017 and $147 in 2016				1,568	1,568
Adjustment for interest rate swap, net of tax of ($64) in 2018, $88 in 2017 and $225 in 2016				84	84
Shares withheld on restricted stock vesting		(23)			(23)
Stock based compensation	$ 1	4,549			4,550
Stock based compensation (in shares)	110,094
Balance at Dec. 31, 2018	$ 227	$ 151,813	136,765	(6,049)	282,756
Balance (in shares) at Dec. 31, 2018	22,700,991
Increase (Decrease) in Stockholders' Equity
Impact due to adoption | ASC 2014-09			377		377
Impact due to adoption | ASU 2018-02			$ 1,129	$ (1,129)	$ (1,129)