Income Taxes - Net Operating Losses Carryforwards Expire (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
U.S. loss carryforwards	$ 63,493
State loss carryforwards	$ 124,466
U.S. federal | Minimum
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, expiration year	2032
U.S. federal | Maximum
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, expiration year	2035
California (U.S.) | Minimum
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, expiration year	2017
California (U.S.) | Maximum
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, expiration year	2036