Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies [Line Items]
Earnings Per Share, Diluted	$ 0.42	$ 0.31	$ 0.36	$ 0.32	$ 0.16	$ 0.50	$ 0.17	$ (0.03)	$ 1.41	$ 0.79	$ 1.11
Marketable securities	$ 22,709				$ 22,264				$ 22,709	$ 22,264
Capitalized data and database costs carrying value	$ 571,449				550,705				$ 571,449	550,705
Subscription-based Revenues Contractual Term In Years									10 years
Employee stock purchase plan percent of stock price at closing date	85.00%								85.00%
Escrow Deposit	$ 340,300				265,600				$ 340,300	265,600
Reserves Incorrect Disposition Of Assets	21,200				20,200				21,200	20,200
Flood [Member]
Significant Accounting Policies [Line Items]
Capitalized data and database costs carrying value	$ 55,416				$ 55,416				$ 55,416	$ 55,416
Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life of other intangible assets, minimum (in years)									20 years
Escrow Deposits, Period Held									5 years
Maximum [Member] | Buildings
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)									40 years
Maximum [Member] | Furniture and equipment
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)									10 years
Maximum [Member] | Capitalized software
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)									10 years
Maximum [Member] | Database Development Costs [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)									20 years
Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life of other intangible assets, minimum (in years)									2 years
Escrow Deposits, Period Held									2 years
Minimum [Member] | Buildings
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)									25 years
Minimum [Member] | Furniture and equipment
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives, minimum (in years)									3 years
Minimum [Member] | Capitalized software
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
Restatement Adjustment [Member]
Significant Accounting Policies [Line Items]
Interest Expense				$ 5,200
Interest Expense Net				$ 3,100
Earnings Per Share, Diluted				$ 0.03