Carrying value as of the balance sheet date of obligations, excluding pension and other postretirement benefits, incurred through that date and payable for perquisites provided to employees pertaining to services received from them. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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- Definition

Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means 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. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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Business and Basis of Presentation - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014 Segment	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Organization And Nature Of Business [Line Items]
Cash, cash equivalents and investments	$ 284,200,000
Cash and cash equivalents	102,754,000	256,965,000	156,185,000	187,661,000
Short-term investments	176,785,000	0
Restricted investments	4,600,000
Number of operating segments	1
Accrued liabilities	13,839,000	14,601,000
Accrued employee compensation		5,000,000
Accounts Payable [Member]
Organization And Nature Of Business [Line Items]
Accrued liabilities		$ 9,600,000