Income taxes - Deferred Tax Liabilities and Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Liabilities
Accelerated depreciation	$ 43,396	$ 40,568
Accelerated amortization of deductible intangibles	427,760	420,301
Other	2,655	5,255
Total deferred tax liabilities	473,811	466,124
Assets
Accrued compensation costs	13,440	15,133
Pension and other post-retirement benefits	34,679	39,769
Loss carryforwards	120,695	132,214
Other	34,044	33,116
Total deferred tax assets	202,858	220,232
Valuation allowance	125,894	136,418
Total net deferred tax (liabilities)	$ (396,847)	$ (382,310)