Consolidated Statements of Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Income Statement [Abstract]
Net sales	$ 92,310		$ 91,241		$ 168,677		$ 158,074
Cost of sales	64,434		63,565		118,955		115,086
Gross profit	27,876		27,676		49,722		42,988
Selling, general and administrative expenses	10,584		9,089		18,213		16,056
Gain on disposal of assets	0		(59)		(24)		(52)
Income from operations	17,292		18,646		31,533		26,984
Interest income, net	71		57		140		91
Other income, net	34		253		13		237
Income before taxes	17,397		18,956		31,686		27,312
Income tax provision	6,034		6,837		10,501		8,053
Net income	$ 11,363		$ 12,119		$ 21,185		$ 19,259
Earnings per share:
Basic (usd per share)	$ 0.21	[1]	$ 0.22	[1]	$ 0.38	[1]	$ 0.35	[1]
Diluted (usd per share)	$ 0.20	[1]	$ 0.22	[1]	$ 0.38	[1]	$ 0.35	[1]
Cash dividends declared per common share	$ 0.09	[1]	$ 0.07	[1]	$ 0.09	[1]	$ 0.07	[1]
Weighted average shares outstanding:
Basic (in shares)	55,004,175	[1]	55,139,577	[1]	55,036,281	[1]	55,140,260	[1]
Diluted (in shares)	55,568,212	[1]	55,725,393	[1]	55,603,979	[1]	55,584,302	[1]

[1] Reflects three-for-two stock split effective July 16, 2014