Income Taxes - Deferred Income Taxes Related to Temporary Differences between Tax Bases of Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax liabilities:
Accelerated depreciation	$ 208,539	$ 195,694
Prepaid costs currently deductible	4,845	4,152
Other	4,703	4,405
Total deferred tax liabilities	218,087	204,251
Deferred tax assets:
Accrued costs not yet deductible	7,796	7,880
Allowance for doubtful accounts	486	484
Deferred revenues	1,774	213
Share-based compensation	1,367	1,045
Total deferred tax assets, net of valuation allowance of $0.2 million in 2018 and $0.8 million in 2017	11,423	9,622
Deferred income taxes, net	$ 206,664	$ 194,629