Acquisition of Florida Chemical Company, Inc. - Pro Forma Results of Operations (Details) (Florida Chemical Company, Inc [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Florida Chemical Company, Inc [Member]
Business Acquisition [Line Items]
Revenue	$ 100,324	$ 100,943	$ 196,174	$ 204,209
Net income	$ 9,099	$ 13,482	$ 18,072	$ 16,986
Earnings per common share:
Basic (in dollars per share)	$ 0.18	$ 0.28	$ 0.36	$ 0.35
Diluted (in dollars per share)	$ 0.17	$ 0.25	$ 0.34	$ 0.34