Cash, Cash Equivalents and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Cash, Cash Equivalents and Marketable Securities [Abstract]

Summary of investments in cash, cash equivalents and marketable securities

2. Cash, Cash Equivalents and Marketable Securities

The following table summarizes our investments in cash equivalents and marketable securities held by investment managers and overnight investments:

	December 31,
	2017			2016
	(in thousands)
Overnight holdings:
Money market funds (cash equivalents)	$	338,112		$	255,091
Investment holdings:
Money market funds (cash equivalents)	22,634			28,231
Marketable securities	1,960			1,851
	362,706			285,173
Cash held in demand accounts	26,700			25,758
Outstanding checks	(33,186		)	(23,046		)
Total cash, cash equivalents and marketable securities	$	356,220		$	287,885
Cash and cash equivalents	$	354,260		$	286,034
Marketable securities	1,960			1,851
Total cash, cash equivalents and marketable securities	$	356,220		$	287,885

Our cash and overnight holdings fluctuate based on the timing of the client’s payroll processing cycle. Included in the cash balance as of December 31, 2017 and December 31, 2016, are $271.5 million and $221.7 million, respectively, in withholdings associated with federal and state income taxes, employment taxes and other payroll deductions, as well as $23.6 million and $21.3 million, respectively, in client prepayments.