CONDENSED CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Capital Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Balance, beginning of period at Dec. 31, 2018		$ 18,395	$ 132,360	$ 776,403	$ (78,834)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for vested restricted stock units, net of shares withheld for taxes		133	(7,273)
Stock options exercised		8	277
Shares issued for employee stock purchase plan		7	580
Shares issued to directors		3	(3)
Equity compensation expense			2,476
Net income	$ 28,399			28,399
Other comprehensive loss	(4,589)				(4,589)
Balance, end of period at Mar. 31, 2019	868,322	18,546	128,417	804,782	(83,423)
Balance, beginning of period at Dec. 31, 2019	933,900	18,577	138,526	823,702	(46,905)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for vested restricted stock units, net of shares withheld for taxes		79	(5,076)
Stock options exercised		0	0
Shares issued for employee stock purchase plan		6	658
Shares issued to directors		0	0
Equity compensation expense			3,127
Net income	13,259			13,259
Other comprehensive loss	(8,144)				(8,144)
Balance, end of period at Mar. 31, 2020	$ 937,809	$ 18,662	$ 137,235	$ 836,961	$ (55,049)