CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net income	$ 2,365	$ 13,759
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	2,092	1,772
Depreciation	6,567	4,373
Amortization of intangibles	1,827	542
Amortization of premiums on short-term investments	871
Realized losses on short-term investments	4
Tax payments for equity award issuances	88
Deferred income taxes	(1,252)	(493)
Excess tax benefits from share-based compensation	(911)
Loss on disposal of long-lived assets		4
Gain on disposal of equipment	(534)
Changes in assets and liabilities:
Accounts receivable	8,128	(21,703)
Prepaid expenses and other current assets	(5,054)	277
Income taxes receivable	2,037	6,797
Other assets	78	(171)
Accounts payable	(2,194)	(1,685)
Accrued compensation	(3,877)	(6,368)
Other liabilities	2,676	655
Deferred rent	(149)	(109)
Deferred revenue	1,537	613
Income taxes payable		2,554
Net cash provided by operating activities	14,299	817
Cash flows from investing activities:
Purchases of short-term investments	(80,065)
Sales and maturities of short-term investments	84,671
Purchases of property and equipment	(4,053)	(1,338)
Investment in capitalized software	(2,790)	(5,158)
Net cash used in investing activities	(2,237)	(6,496)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of underwriters' discount		362,082
Proceeds from issuance of treasury stock, net of underwriters' discount		282,172
Payment of offering costs		(3,002)
Repayment of credit facility borrowings	(3,750)	(5,000)
Proceeds from exercise of stock options	3,841
Capital lease obligations paid	(31)	(26)
Tax payments for equity award issuances	(182)
Excess tax benefits from share-based compensation	911
Net cash provided by financing activities	789	636,226
Increase in cash and cash equivalents	12,851	630,547
Cash and cash equivalents, beginning of period	114,034	162,567
Cash and cash equivalents, end of period	126,885	793,114
Supplemental cash flow disclosure:
Cash paid during the period for: Income taxes, net of refunds	861	1,583
Cash paid during the period for: Interest	1,195	1,076
Noncash investing activities:
Accounts payable for purchases of and investment in property, equipment and capitalized software	933	1,557
Accrued compensation for investment in capitalized software	$ 53	464
Offering costs not yet paid		$ 2,180