Fair Value Measurements - Valuation of Financial Instruments by Pricing Levels (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivative assets (liabilities):
Derivative assets (liabilities)	$ (9,410)	$ 2,603
Swap [Member]
Derivative assets (liabilities):
Derivative assets (liabilities)	(9,410)	2,603
Fair Value, Inputs, Level 1 [Member]
Derivative assets (liabilities):
Derivative assets (liabilities)	0	0
Fair Value, Inputs, Level 1 [Member] | Swap [Member]
Derivative assets (liabilities):
Derivative assets (liabilities)	0	0
Fair Value, Inputs, Level 2 [Member]
Derivative assets (liabilities):
Derivative assets (liabilities)	(9,410)	2,603
Fair Value, Inputs, Level 2 [Member] | Swap [Member]
Derivative assets (liabilities):
Derivative assets (liabilities)	(9,410)	2,603
Fair Value, Inputs, Level 3 [Member]
Derivative assets (liabilities):
Derivative assets (liabilities)	0	0
Fair Value, Inputs, Level 3 [Member] | Swap [Member]
Derivative assets (liabilities):
Derivative assets (liabilities)	$ 0	$ 0