Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended									3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 5.68% note, due June 30, 2026 [Member]	Dec. 31, 2013 5.68% note, due June 30, 2026 [Member]	Mar. 31, 2014 Uncollateralized Senior Notes Due On Two Thousand Twenty Nine [Member]	Sep. 05, 2013 Aggregate Unsecured Senior Notes [Member]	Mar. 31, 2014 Uncollateralized Senior Note Two Due on December Two Thousand Twenty Eight [Member]	Dec. 31, 2013 Uncollateralized Senior Note Two Due on December Two Thousand Twenty Eight [Member]	Mar. 31, 2014 Convertible Debt Securities [Member]
Debt Instrument [Line Items]
Long term debt maximum borrowing capacity						$ 50,000,000.0	$ 70,000,000
Total long-term debt	121,200,000		122,000,000	29,000,000	29,000,000			20,000,000	20,000,000
Long-term debt, interest percentage				5.68%		3.88%		3.73%	3.73%
Repayments of Long-term Debt	196,000	15,000
Debt Conversion, Converted Instrument, Amount										537,000
Repayments of Convertible Debt										$ 109,000