Debt and Financing Arrangements - Additional Information (Detail) (USD $)	12 Months Ended											12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2013 Senior Notes under Master Shelf Agreement [Member]	Dec. 31, 2012 Senior Notes under Master Shelf Agreement [Member]	Jan. 31, 2008 Senior Notes under Master Shelf Agreement [Member]	Nov. 30, 2007 Senior Notes under Master Shelf Agreement [Member]	Apr. 30, 2005 Senior Notes under Master Shelf Agreement [Member]	Sep. 20, 2002 Senior Notes under Master Shelf Agreement [Member]	Dec. 31, 2013 Revolving credit facility [Member]	Dec. 31, 2013 Credit Agreement with Banks [Member]	Dec. 31, 2012 Credit Agreement with Banks [Member]	Dec. 31, 2013 Credit Agreement with Banks [Member] Minimum [Member]	Dec. 31, 2013 Credit Agreement with Banks [Member] Maximum [Member]	Dec. 31, 2013 Credit Agreement with Banks [Member] LIBOR Rate Margin [Member] Minimum [Member]	Dec. 31, 2013 Credit Agreement with Banks [Member] LIBOR Rate Margin [Member] Maximum [Member]	Dec. 31, 2013 Credit Agreement with Banks [Member] Base rate margin [Member] Minimum [Member]	Dec. 31, 2013 Credit Agreement with Banks [Member] Base rate margin [Member] Maximum [Member]
Line of Credit Facility [Line Items]
Borrowing capacity under credit agreement												$ 200,000,000
Line of credit facility expiration year and month												2018-06
Additional borrowing capacity under revolving credit facility												40,000,000
Rate margin																	1.25%	2.50%	0.125%	0.50%
Letter of credit fee				1.375%	2.625%
Letter of credit unused portion fee															0.20%	0.325%
Letter of credit facility outstanding amount	59,100,000	49,100,000
Total debt	76,883,000	60,705,000				28,571,000	50,715,000						48,312,000	9,990,000
Senior notes issued, value								25,000,000	25,000,000		100,000,000
Senior notes authorized amount										150,000,000	125,000,000
Interest rate on notes								6.17%	6.14%		7.38%
Senior credit facility, Interest rate terms description						Payments due under the $100 million Senior Notes were interest only until June 30, 2006 and at that time semi-annual principal payments began with the final payment due December 2013. The November 2007 issuance of $25 million Senior Notes has a fixed interest rate of 6.14 percent. The January 2008 issuance of $25 million Senior Notes has a fixed interest rate of 6.17 percent. Payments due for both $25 million issuances were interest only until June 30, 2011 and at that time semi-annual principal payments began with the final payments due January 1, 2018.
Cash paid for interest	6,100,000	7,300,000	9,000,000
Estimated fair value of total debt	$ 78,000,000	$ 63,500,000