Income Taxes - Tax Benefits of NOL Carryforwards (Detail) $ in Millions	Dec. 31, 2016 USD ($)
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, or NOLs	$ 126.0
2020 [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, or NOLs	0.1
2021 [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, or NOLs	0.1
2022 [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, or NOLs	0.1
2023 [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, or NOLs	0.1
2024 [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, or NOLs	0.1
2025 [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, or NOLs	58.1
2036 [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, or NOLs	$ 67.4