Annual report pursuant to section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Details)

Summary of Significant Accounting Policies - Additional Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011 Money Market Balances Reclassified As Due From Clearing Broker in Prior Years [Member]	Dec. 31, 2010 Money Market Balances Reclassified As Due From Clearing Broker in Prior Years [Member]	Dec. 31, 2009 Money Market Balances Reclassified As Due From Clearing Broker in Prior Years [Member]
Prior period reclassification adjustment				$ 8,969	$ 6,096	$ 1,984
Reclassification changes in cash flow from operating activities	2,873	4,112
Money market funds	$ 8,969		$ 8,882

- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References + Details