Shareholders' equity - Narrative (Detail)			3 Months Ended	12 Months Ended
	Mar. 01, 2018 shares	May 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) adjustment $ / shares shares	May 04, 2010 shares
Stockholders Equity Note [Line Items]
Common stock, authorized (in shares)				800,000,000	800,000,000
Preferred stock, authorized (in shares)				2,000,000	2,000,000
Common stock, outstanding (in shares)				215,800,000	214,900,000
Treasury stock (in shares)				108,660,002	109,487,979
Preferred stock, issued (in shares)				0	0
Preferred stock, outstanding (in shares)				0	0
Stock options outstanding excluded from calculation of diluted earnings per share (in shares)				205,000,000	190,000,000	150,000,000
Shares approved to be repurchased under share repurchase program, amount | $			$ 300,000,000.0
Share repurchase program, period in force			3 years
Shares repurchased under share repurchase program (in shares)				500,000	1,500,000	7,000,000
Cost of common shares repurchased | $				$ 5,831,000	$ 23,480,000	$ 161,891,000
Remaining authorized repurchase amount | $				$ 279,100,000
Shares granted with aggregate target awards (in shares)	600,000
Spin-off of Publishing businesses | $					$ 1,513,881,000	$ 45,128,000
Minimum
Stockholders Equity Note [Line Items]
Number of units ultimately paid for performance share awards of target (as a percent)				0
Maximum
Stockholders Equity Note [Line Items]
Number of units ultimately paid for performance share awards of target (as a percent)				2
Stock Options
Stockholders Equity Note [Line Items]
Award vesting period				4 years
Stock options outstanding (in shares)				400,000	1,300,000
Stock options outstanding, weighted average exercise price (in dollars per share) | $ / shares				$ 8.56	$ 8.25
Weighted average remaining contractual life				3 months 30 days
Aggregate intrinsic value | $				$ 900,000
Stock options exercised (in shares)				800,000	800,000	200,000
Stock options exercised, weighted average exercise price (in dollars per share) | $ / shares				$ 8.10	$ 9.07	$ 11.03
Intrinsic value of all stock options exercised | $				$ 5,200,000	$ 5,300,000	$ 2,300,000
Stock Options | Employee
Stockholders Equity Note [Line Items]
Shares reserved for issuance (in shares)							60,000,000.0
Performance Based Awards
Stockholders Equity Note [Line Items]
Award vesting period				3 years
Restricted Stock Units (RSUs) | Employee
Stockholders Equity Note [Line Items]
Number of shares of common stock received for each RSU granted				1
Award vesting percentage				25.00%
Performance Shares
Stockholders Equity Note [Line Items]
Spin-off adjustment, conversion factor				1.59
Unrecognized compensation cost related to non-vested share-based compensation | $				$ 1,100,000
Unrecognized compensation cost related to non-vested share-based compensation for options, recognition period				1 year
Restricted Stock and Restricted Stock Units
Stockholders Equity Note [Line Items]
Unrecognized compensation cost related to non-vested share-based compensation | $				$ 15,100,000
Unrecognized compensation cost related to non-vested share-based compensation for options, recognition period				2 years 6 months 13 days
Publishing
Stockholders Equity Note [Line Items]
Number of adjustments to retained earnings | adjustment						2
Adjustments to Postretirement Benefits Transferred, Spinoff Transaction | Retirement Plans | Publishing
Stockholders Equity Note [Line Items]
Spin-off of Publishing businesses | $						$ 7,700,000
Adjustments to Deferred Tax Assets and Liabilities Transferred, Spinoff Transaction | Publishing
Stockholders Equity Note [Line Items]
Spin-off of Publishing businesses | $						34,800,000
Retained earnings
Stockholders Equity Note [Line Items]
Spin-off of Publishing businesses | $					$ 1,513,881,000	42,486,000
Retained earnings | Cars.com
Stockholders Equity Note [Line Items]
Spin-off of Publishing businesses | $		$ 1,500,000,000
Retained earnings | Publishing
Stockholders Equity Note [Line Items]
Spin-off of Publishing businesses | $						$ 42,500,000
Cars.com | Performance Shares
Stockholders Equity Note [Line Items]
Adjustment due to spin-off of Publishing (in shares)				0	178,775	0
Cars.com | Restricted Stock and Restricted Stock Units
Stockholders Equity Note [Line Items]
Adjustment due to spin-off of Publishing (in shares)				0	606,377	0