CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenue		$ 110,578	$ 123,825	$ 218,884	$ 226,482
Expenses:
Cost of revenue	[1]	37,198	43,214	75,483	85,137
Sales and marketing	[1]	8,849	6,116	16,436	12,675
Research and development	[1]	7,282	7,711	15,070	13,643
General and administrative	[1]	35,874	31,461	71,719	68,013
Depreciation and amortization		12,479	8,496	24,964	16,890
Total operating expenses		101,682	96,998	203,672	196,358
Income from operations		8,896	26,827	15,212	30,124
Other income and (expenses):
Realized losses on short-term investments		0	(1)	0	(5)
(Loss) Gain on disposal of equipment		(138)	0	(138)	534
Interest income		1,342	1,532	2,680	2,974
Interest expense		(1,519)	(1,245)	(2,932)	(2,504)
Income before taxes		8,581	27,113	14,822	31,123
Provision for income taxes		3,095	10,862	5,694	12,507
Net income		5,486	16,251	9,128	18,616
Net income attributable to common stockholders, basic and diluted		$ 5,338	$ 16,179	$ 8,913	$ 18,537
Net income per share attributable to common stockholders, basic and diluted:
Basic net income per share (in dollars per share)		$ 0.04	$ 0.11	$ 0.06	$ 0.12
Diluted net income per share (in dollars per share)		$ 0.04	$ 0.11	$ 0.06	$ 0.12
Weighted average shares of common stock outstanding:
Basic (in shares)		142,632	151,712	143,680	151,497
Diluted (in shares)		143,072	152,706	144,123	152,548

[1] (1)Includes stock-based compensation expense as follows: Cost of revenue$410 $121 $715 $240 Sales and marketing505 152 895 306 Research and development307 499 580 741 General and administrative2,525 1,364 5,154 2,941 Total stock-based compensation expense$3,747 $2,136 $7,344 $4,228