Significant Accounting Policies (Narrative) (Details) $ in Thousands		3 Months Ended								12 Months Ended					24 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2018 USD ($) customer	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) customer	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment customer	Dec. 31, 2017 USD ($) segment customer	Dec. 31, 2016 USD ($) segment customer	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)
Significant Accounting Policies [Line Items]
Indemnification exposure, including interest for discontinued operating unit		$ 25,000								$ 25,000
(Loss)/income from discontinued operations, net of tax		$ (412)	$ (84)	$ (16)	$ (75)	$ (106)	$ (74)	$ 78	$ 2,417	$ (587)	$ 2,315	$ (1,466)
Number of customers | customer		1,000,000								1,000,000
Provision for income taxes										$ (45,691)	(18,172)	(54,524)
Deferred income tax (benefit)										26,940	(40,769)	18,213
Accounts payable and other accrued expenses		$ 166,258				145,655				166,258	145,655
Capitalized data and database costs carrying value		$ 658,735				636,948				$ 658,735	636,948
Employee stock purchase plan percent of stock price at closing date		85.00%								85.00%
Escrow deposits		$ 696,000				961,500				$ 696,000	961,500
Reserves incorrect disposition of assets		21,200				21,700				21,200	21,700
Share-based compensation true-up (less than)										37,196	35,867	39,849
Gain/(loss) from sale of discontinued operations, net of tax										0	313	$ (1,930)
Disposal Group, Including Discontinued Operation, Assets, Current		600				400				600	400
Disposal group, liabilities current		2,200				1,800				2,200	$ 1,800
Contract liabilities	$ 840,400	833,000								$ 833,000
Number of Reportable Segments | segment										2	2	2
Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life of other intangible assets, minimum (in years)										25 years
Escrow deposits, period held by the Company (in business days)										5 years
Maximum [Member] | Buildings [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)										40 years
Maximum [Member] | Furniture and equipment [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)										10 years
Maximum [Member] | Capitalized software [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)										15 years
Maximum [Member] | Database Development Costs [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)										25 years
Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life of other intangible assets, minimum (in years)										2 years
Escrow deposits, period held by the Company (in business days)										2 years
Minimum [Member] | Buildings [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)										25 years
Minimum [Member] | Furniture and equipment [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)										3 years
Minimum [Member] | Capitalized software [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)										3 years
Minimum [Member] | Database Development Costs [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)										5 years
Flood data [Member]
Significant Accounting Policies [Line Items]
Capitalized data and database costs carrying value		$ 55,416				$ 55,416				$ 55,416	$ 55,416
Accounting Standards Update 2017-07 [Member]
Significant Accounting Policies [Line Items]
Reclassification of net periodic benefit costs from adoption of ASU 2017-07											800	$ 3,400	$ 500
Accounting Standards Update 2016-09 [Member]
Significant Accounting Policies [Line Items]
Deferred income tax (benefit)											(2,500)
Share-based compensation true-up (less than)											$ 100
Accounting Standards Update 2014-09 [Member]
Significant Accounting Policies [Line Items]
Contract liabilities result of change in accounting for contracts containing material rights the client received due to having contract	(23,200)
Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Significant Accounting Policies [Line Items]
Number of customers | customer		0				1				0	1	2
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Ten Largest Clients [Member]
Significant Accounting Policies [Line Items]
Concentration risk, percentage										31.30%	38.70%	43.00%
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Client A [Member]
Significant Accounting Policies [Line Items]
Concentration risk, percentage										11.10%		14.00%
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Client B [Member]
Significant Accounting Policies [Line Items]
Concentration risk, percentage												11.50%
Employer And Litigation Services [Member] | Discontinued Operations, Disposed of by Sale [Member]
Significant Accounting Policies [Line Items]
(Loss)/income from discontinued operations, net of tax											$ (381)	$ (1,000)
Asset Management and Processing Solutions [Member] | Discontinued Operations, Disposed of by Sale [Member]
Significant Accounting Policies [Line Items]
(Loss)/income from discontinued operations, net of tax												(500)
Gain recorded on pre-tax legal settlement											4,500
Adoption Adjustments [Member] | Accounting Standards Update 2014-09 [Member]
Significant Accounting Policies [Line Items]
Provision for income taxes										$ (7,134)
Accounts payable and other accrued expenses		$ (386)								(386)
Contract liabilities	(31,600)
Capitalized Contract Cost, Gross	$ 1,600
Accounts Payable and Accrued Liabilities [Member]
Significant Accounting Policies [Line Items]
Reserves incorrect disposition of assets		$ 9,200				$ 9,400				$ 9,200	9,400
Restatement Adjustment [Member]
Significant Accounting Policies [Line Items]
Provision for income taxes							$ (3,000)	$ (1,300)					$ (9,400)	$ (2,000)	$ (7,400)
Deferred income tax (benefit)											$ (4,300)	$ (3,100)