CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 17,369	$ 26,423
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	12,325	6,352
Depreciation	27,129	20,368
Amortization of intangibles	11,385	5,426
Amortization of premiums on short-term investments	1,571	2,502
Realized gains on short-term investments	0	(4)
Tax payments for equity award issuances	0	95
Deferred income taxes	(1,540)	(3,110)
Excess tax benefits from stock-based compensation	0	(1,135)
Loss (Gain) on disposal of equipment	381	(534)
Change in fair value of contingent consideration	(2,900)	706
Bad debt expense	0	79
Changes in assets and liabilities:
Accounts receivable	5,259	1,332
Prepaid expenses and other current assets	1,931	(3,604)
Income taxes receivable	11,174	7,677
Other assets	(2,722)	4,189
Accounts payable	5,653	(5,903)
Accrued compensation	1,346	2,090
Other liabilities	(4,210)	5,866
Deferred rent	(696)	(557)
Deferred revenue	(2,507)	361
Net cash provided by operating activities	80,948	68,619
Cash flows from investing activities:
Maturities of short-term investments	150,696	248,998
Sales of short-term investments	0	31,549
Purchases of short-term investments	0	(164,737)
Purchases of property and equipment	(17,544)	(11,267)
Investment in capitalized software	(21,741)	(14,220)
Acquisitions, net of cash acquired of $1,535	(3,490)	0
Net cash provided by investing activities	107,921	90,323
Cash flows from financing activities:
Repurchase of common stock	(64,986)	(51,118)
Repayment of credit facility borrowings	(22,500)	(11,250)
Proceeds from exercise of stock options	3,781	5,111
Acquisition-related contingent consideration	0	(2,300)
Capital lease obligations paid	(84)	(31)
Tax payments for equity award issuances	(208)	(137)
Excess tax benefits from stock-based compensation	0	1,135
Net cash used in financing activities	(83,997)	(58,590)
Increase in cash and cash equivalents	104,872	100,352
Cash and cash equivalents, beginning of period	127,683	114,034
Cash and cash equivalents, end of period	232,555	214,386
Supplementary cash flow disclosure:
Cash paid during the period for: Income taxes, net of refunds	725	10,014
Cash paid during the period for: Interest	4,416	3,600
Non-cash investing activities:
Accruals for purchases of property, equipment	8,295	816
Accruals for investment in capitalized software	$ 3,892	$ 492