Condensed Statements of Income (Detail) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2008
Administrative expenses	$ (1,853,646)	$ (1,807,615)	$ (2,006,127)	$ (2,405,784)	$ (2,630,168)	$ (2,059,027)	$ (1,834,465)	$ (2,097,834)	$ (2,239,462)	$ (1,498,306)	$ (1,339,062)	$ (1,573,312)	$ (8,073,172)	$ (8,621,494)	$ (6,650,142)
Other expenses:
Change in fair value of warrant													(106,536)	(124,000)	3,062,575
Gain (Loss) on extinguishment of warrant liabilities													(8,369)	73,291	88,777
NET INCOME	13,233,558	13,938,895	15,675,810	13,311,187	15,793,687	17,226,638	13,446,666	11,475,012	12,727,388	13,528,083	14,366,076	12,511,986	56,159,450	57,942,003	53,133,533	11,701,879
Parent
Administrative expenses													(2,818,130)	(3,397,929)	(2,267,880)
Other expenses:
Change in fair value of warrant													(106,536)	(124,000)	3,062,575
Gain (Loss) on extinguishment of warrant liabilities													(8,369)	73,291	88,777
Equity in income of subsidiaries													59,092,485	61,390,641	52,250,061
NET INCOME													$ 56,159,450	$ 57,942,003	$ 53,133,533