Quarterly Results of Operations (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Summary of Quarterly Results of Operations

	2016												2015
	First			Second			Third			Fourth			First			Second			Third			Fourth
	Quarter			Quarter			Quarter			Quarter			Quarter			Quarter			Quarter			Quarter
	(in thousands, except per share data)
Operating revenues	$	278,828		$	290,596		$	288,433		$	292,812		$	262,769		$	270,580		$	268,771		$	272,893
Cost of revenues		63,172			62,130			62,986			63,819			69,904			67,394			65,593			64,804
Selling and marketing		41,689			41,854			41,514			41,609			41,648			42,028			38,809			39,809
Research and development		18,928			18,566			18,750			18,960			23,189			20,807			15,548			17,776
General and administrative		21,890			22,019			21,859			21,467			20,377			22,080			19,960			23,590
Amortization of intangible assets		11,840			11,943			11,752			11,498			11,702			11,695			11,710			11,803
Depreciation and amortization of    property, equipment and    leasehold improvements		8,168			8,393			8,312			9,447			7,207			8,065			8,049			7,568
Total operating expenses		165,687			164,905			165,173			166,800			174,027			172,069			159,669			165,350
Operating income		113,141			125,691			123,260			126,012			88,742			98,511			109,102			107,543
Interest income		(621	)		(585	)		(799	)		(901	)		(204	)		(185	)		(285	)		(492	)
Interest expense		22,904			22,918			26,790			29,039			11,108			11,116			17,267			22,896
Other expense (income)		81			2,814			(253	)		779			178			164			(6,922	)		(297	)
Other expense (income), net		22,364			25,147			25,738			28,917			11,082			11,095			10,060			22,107
Income from continuing operations    before provision for income taxes		90,777			100,544			97,522			97,095			77,660			87,416			99,042			85,436
Provision for income taxes		30,410			33,587			32,241			28,845			28,036			31,399			34,644			25,437
Income from continuing operations		60,367			66,957			65,281			68,250			49,624			56,017			64,398			59,999
Income (loss) from discontinued    operations, net of income taxes		—			—			—			—			(5,797	)		—			—			(593	)
Net income	$	60,367		$	66,957		$	65,281		$	68,250		$	43,827		$	56,017		$	64,398		$	59,406
Earnings per basic common share
From continuing operations	$	0.61		$	0.69		$	0.69		$	0.73		$	0.44		$	0.50		$	0.59		$	0.59
From discontinued operations		—			—			—			—			(0.05	)		—			—			(0.01	)
Earnings per basic common share	$	0.61		$	0.69		$	0.69		$	0.73		$	0.39		$	0.50		$	0.59		$	0.58
Earnings per diluted common share
From continuing operations	$	0.60		$	0.69		$	0.68		$	0.73		$	0.44		$	0.50		$	0.59		$	0.58
From discontinued operations		—			—			—			—			(0.05	)		—			—			(0.01	)
Earnings per diluted commons hare	$	0.60		$	0.69		$	0.68		$	0.73		$	0.39		$	0.50		$	0.59		$	0.57
Weighted average shares outstanding    used in computing per share data
Basic		99,425			96,412			94,823			93,327			112,520			112,143			108,773			102,837
Diluted		99,998			96,888			95,473			93,845			113,522			112,931			109,440			103,590