Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING ACTIVITIES:
Net income (loss)	$ 422	$ (18,673)	$ (9,249)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	31,010	12,517	8,438
Stock-based compensation	30,584	23,846	6,352
Loss (gain) on disposal of property and equipment, net	58	202	(7)
Change in fair value of preferred stock warrant liabilities	0	732	4,121
Change in fair value of contingent consideration	306	66	0
Unrealized foreign currency (gains) losses, net	(72)	(763)	68
Deferred income taxes	(5,286)	(145)	0
Changes in operating assets and liabilities, net of effect of business acquisitions:
Accounts receivable	(71,796)	(38,023)	(27,102)
Prepaid expenses and other assets	(1,073)	(2,152)	(1,966)
Accounts payable and accrued expenses	93,135	29,861	39,168
Other liabilities	(432)	(823)	1,269
Net cash provided by operating activities	76,856	6,645	21,092
INVESTING ACTIVITIES:
Purchases of property and equipment, net	(20,104)	(10,706)	(6,785)
Capitalized internal use software development costs	(8,333)	(8,779)	(3,926)
Acquisitions, net of cash acquired	(8,647)	(3,983)	0
Investments in available-for-sale securities	(48,801)	0	0
Maturities of available-for-sale securities	12,001	0	0
Change in restricted cash	1,023	345	(1,151)
Net cash used in investing activities	(72,861)	(23,123)	(11,862)
FINANCING ACTIVITIES:
Proceeds from the issuance of common stock in initial public offering, net of underwriting discounts and commissions	0	89,733	0
Payments of initial public offering costs	0	(3,037)	(496)
Proceeds from exercise of stock options	13,533	3,498	866
Proceeds from issuance of common stock under employee stock purchase plan	2,040	0	0
Taxes paid related to net share settlement	0	(2,324)	0
Repayment of debt and capital lease obligations	(105)	(4,076)	(1,166)
Net cash provided by (used in) financing activities	15,468	83,794	(796)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	(160)	(76)	(94)
CHANGE IN CASH AND CASH EQUIVALENTS	19,303	67,240	8,340
CASH AND CASH EQUIVALENTS--Beginning of period	97,196	29,956	21,616
CASH AND CASH EQUIVALENTS--End of period	116,499	97,196	29,956
SUPPLEMENTAL DISCLOSURES OF OTHER CASH FLOW INFORMATION:
Cash paid for income taxes	1,069	403	307
Cash paid for interest	62	122	241
Capitalized assets financed by accounts payable and accrued expenses	342	1,872	194
Leasehold improvements paid by landlord	0	803	0
Capitalized stock-based compensation	819	624	181
Conversion of preferred stock to common stock	0	52,571	0
Reclassification of preferred stock warrant liabilities to additional-paid-in-capital	0	6,183	0
Reclassification of deferred offering costs to additional-paid-in-capital	0	3,533	0
Deferred offering costs included in accounts payable and accrued expenses	0	0	865
Common stock and options issued for business acquisitions	76,534	13,342	0
Conversion of contingent consideration to common stock	$ 25,608	$ 0	$ 0