Royalty Arrangement with Bristol Myers Squibb Company - Additional Information (Detail) (USD $)	3 Months Ended								9 Months Ended		12 Months Ended		9 Months Ended		12 Months Ended
	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, 2011	Dec. 31, 2010	Dec. 31, 2012	Mar. 31, 2011	Dec. 31, 2011 Bristol Myers Squibb Company	Dec. 31, 2010 Bristol Myers Squibb Company	Dec. 31, 2012 Bristol Myers Squibb Company	Mar. 31, 2011 Bristol Myers Squibb Company	Mar. 31, 2008 Bristol Myers Squibb Company First $500 million of annual net sales	Mar. 31, 2008 Bristol Myers Squibb Company Next $500 million of annual net sales	Mar. 31, 2008 Bristol Myers Squibb Company Annual net sales in excess of $1 billion for each year from January 1, 2008 until December 31, 2013
Legal Settlement By Party [Line Items]
Bristol Settlement agreement, royalty payment rate																	1.80%	2.00%	4.00%
Annual net sales																	$ 500,000,000	$ 500,000,000	$ 1,000,000,000
Royalty revenue recognized	9,104,000	3,981,000	3,865,000	3,482,000	4,051,000	2,889,000	3,295,000	2,756,000	10,235,194	9,573,770	20,432,348	12,329,627	8,769,000	7,739,000	14,753,000	10,251,000
Percentage royalty revenue paid to University of Michigan															15.00%
Royalty expense													$ 1,315,000	$ 1,161,000	$ 2,213,000	$ 1,537,000