Long-Term Debt - Redemption Price Percentage (Detail) - Senior Notes - 6% senior notes due 2022	12 Months Ended
	Dec. 31, 2017
2018
Long Term Debt And Capital Lease Obligations [Line Items]
Redemption price (as a percent)	102.00%
2019
Long Term Debt And Capital Lease Obligations [Line Items]
Redemption price (as a percent)	101.00%
2020 and thereafter
Long Term Debt And Capital Lease Obligations [Line Items]
Redemption price (as a percent)	100.00%