CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenue		$ 115,855	$ 105,013	$ 334,739	$ 331,495
Expenses:
Cost of revenue	[1]	38,431	35,433	113,914	120,570
Sales and marketing	[1]	7,929	7,037	24,365	19,712
Research and development	[1]	5,780	7,404	20,850	21,047
General and administrative	[1]	36,283	37,209	108,002	105,222
Depreciation and amortization		13,550	8,904	38,514	25,794
Total operating expenses		101,973	95,987	305,645	292,345
Income from operations		13,882	9,026	29,094	39,150
Other income and (expenses):
Realized gains on short-term investments		0	9	0	4
(Loss) Gain on disposal of equipment		(243)	0	(381)	534
Interest income		1,365	1,450	4,045	4,424
Interest expense		(1,617)	(1,302)	(4,549)	(3,806)
Income before taxes		13,387	9,183	28,209	40,306
Provision for income taxes		5,146	1,376	10,840	13,883
Net income		8,241	7,807	17,369	26,423
Net income attributable to common stockholders, basic and diluted		$ 7,968	$ 7,771	$ 16,905	$ 26,308
Net income per share attributable to common stockholders, basic and diluted:
Basic net income per share (in dollars per share)		$ 0.06	$ 0.05	$ 0.12	$ 0.17
Diluted net income per share (in dollars per share)		$ 0.06	$ 0.05	$ 0.12	$ 0.17
Weighted average shares of common stock outstanding:
Basic (in shares)		141,226	150,732	142,861	151,240
Diluted (in shares)		141,699	151,562	143,327	152,122

[1] (1)Includes stock-based compensation expense as follows: Cost of revenue$474 $94 $1,189 $334 Sales and marketing561 140 1,456 446 Research and development349 186 929 927 General and administrative3,597 1,704 8,751 4,645 Total stock-based compensation expense$4,981 $2,124 $12,325 $6,352