Consolidated Statements of Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Income Statement [Abstract]
Net sales	$ 91,241		$ 83,333		$ 158,074		$ 148,290
Cost of sales	63,565		62,230		115,086		113,669
Gross profit	27,676		21,103		42,988		34,621
Selling, general and administrative expenses	9,089		6,899		16,056		12,880
Loss (gain) on disposal of assets	(59)		10		(52)		(13)
Income from operations	18,646		14,194		26,984		21,754
Interest expense	0		(11)		(1)		(27)
Interest income	57		2		92		15
Other income (expense), net	253		(51)		237		(3)
Income before taxes	18,956		14,134		27,312		21,739
Income tax provision	6,837		4,837		8,053		7,875
Net income	$ 12,119		$ 9,297		$ 19,259		$ 13,864
Earnings per share:
Basic	$ 0.33	[1]	$ 0.25	[1]	$ 0.52	[1]	$ 0.38	[1]
Diluted	$ 0.33	[1]	$ 0.25	[1]	$ 0.52	[1]	$ 0.37	[1]
Cash dividends declared per common share	$ 0.10	[1]	$ 0.08	[1]	$ 0.10	[1]	$ 0.08	[1]
Weighted average shares outstanding:
Basic	36,759,718	[1]	36,828,650	[1]	36,760,173	[1]	36,854,913	[1]
Diluted	37,150,262	[1]	37,091,528	[1]	37,056,201	[1]	37,124,982	[1]

[1] Reflects three-for-two stock split effective July 2, 2013