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, 2017		$ 18,255	$ 128,933	$ 684,540	$ (65,155)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for vested restricted stock units, net of cancellations for tax withholding		113	(6,520)
Stock options exercised		11	462
Shares issued for employee stock purchase plan		6	535
Shares issued to directors		3	(3)
Shares repurchased	$ (3,000)	(23)	(2,976)
Equity compensation expense			2,673
Net income	26,136			26,136
Other comprehensive income (loss)	7,821				7,821
Balance, end of period at Mar. 31, 2018	799,023	18,365	123,104	714,888	(57,334)
Balance, beginning of period at Dec. 31, 2018	848,324	18,395	132,360	776,403	(78,834)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for vested restricted stock units, net of cancellations for tax withholding		133	(7,273)
Stock options exercised		8	277
Shares issued for employee stock purchase plan		7	580
Shares issued to directors		3	(3)
Shares repurchased		0	0
Equity compensation expense			2,476
Net income	28,399			28,399
Other comprehensive income (loss)	(4,589)				(4,589)
Balance, end of period at Mar. 31, 2019	$ 868,322	$ 18,546	$ 128,417	$ 804,782	$ (83,423)