CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 93,247	$ 185,926
Accounts receivable [less allowance for doubtful accounts of $5,105 in 2018 and $5,427 in 2017]	299,253	246,188
Short-term investments	59,459	43,159
Prepaid expenses	34,985	32,206
Income tax receivable	13,100	11,339
Other current assets	1,944	1,997
Total current assets	501,988	520,815
Accounts receivable, long-term	12,387	12,107
Property and equipment, net	154,464	152,315
Other assets:
Goodwill	740,146	657,987
Other intangibles, net	293,194	229,617
Non-current investments and other assets	57,580	38,510
Total assets	1,759,759	1,611,351
Current liabilities:
Accounts payable	4,839	8,174
Accrued liabilities	52,959	64,675
Deferred revenue	316,084	298,613
Total current liabilities	373,882	371,462
Deferred revenue, long-term	785	1,274
Deferred income taxes	44,803	46,879
Commitments and contingencies
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 and outstanding as of June 30, 2018 and December 31, 2017	481	481
Additional paid-in capital	686,782	626,867
Accumulated other comprehensive loss, net of tax	(46)	(46)
Retained earnings	701,449	624,463
Treasury stock, at cost; 9,517,525 and 10,262,182 shares in 2018 and 2017, respectively	(48,377)	(60,029)
Total shareholders' equity	1,340,289	1,191,736
Total liabilities and shareholders' equity	$ 1,759,759	$ 1,611,351