Schedule I - Condensed Financial Information of Registrant - Additional Information (Detail) (Parent company [Member], USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Parent company [Member]
Condensed Financial Information Of Registrant [Line Items]
Amount guaranteed for subsidiaries credit terms	$ 44,700,000
Amount guaranteed for subsidiaries insurance bonds	12,700,000
Shares owned by a subsidiary of LSB	2,451,527	2,451,527
Interest expense incurred from subsidiaries	1,307,000	1,200,000	1,173,000
Interest income earned from subsidiaries	2,168,000	1,262,000	956,000
Dividend received from a subsidiary	$ 24,400,000	$ 0	$ 0