Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 603,623	$ 232,682
Accounts receivable (less allowance for losses and sales adjustments of $9,255 in 2020 and $5,738 in 2019)	382,319	374,089
Short-term investments	72,187	39,399
Prepaid expenses	30,864	24,717
Income tax receivable	21,598	6,482
Other current assets	2,479	2,328
Total current assets	1,113,070	679,697
Accounts receivable, long-term	21,417	22,432
Operating lease right-of-use assets	18,734	18,992
Property and equipment, net	168,004	171,861
Other assets:
Goodwill	838,428	840,117
Other intangibles, net	331,189	378,914
Non-current investments	82,640	42,235
Other non-current assets	33,792	37,366
Total assets	2,607,274	2,191,614
Current liabilities:
Accounts payable	14,011	14,977
Accrued liabilities	83,084	75,234
Operating lease liabilities	5,904	6,387
Deferred revenue	461,278	412,495
Total current liabilities	564,277	509,093
Revolving line of credit	0	0
Deferred revenue, long-term	100	199
Deferred income taxes	40,507	48,442
Operating lease liabilities, long-term	16,279	16,822
Commitments and contingencies	0	0
Shareholders' equity:
Preferred stock, $10.00 par value; 1,000,000 shares authorized; none issued	0	0
Common stock, $0.01 par value; 100,000,000 shares authorized; 48,147,969 shares    issued in 2020 and 2019	481	481
Additional paid-in capital	905,332	739,478
Accumulated other comprehensive loss, net of tax	(46)	(46)
Retained earnings	1,112,156	917,336
Treasury stock, at cost; 7,608,627 and 8,839,352 shares in 2020 and 2019, respectively	(31,812)	(40,191)
Total shareholders' equity	1,986,111	1,617,058
Liabilities and Shareholders' equity, Total	$ 2,607,274	$ 2,191,614