Fair Value Measurements - Schedule of Fair Value of Long-term Borrowings (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Long-term Borrowings:
Carrying amount of senior notes	$ 304,489	$ 303,416
5.0% Exchangeable Senior Notes due March 2021 [Member] | Exchangeable Senior Notes [Member] | Significant Other Observable Inputs (Level 2) [Member]
Long-term Borrowings:
Carrying amount of senior notes	82,249	81,576
Estimated fair value of senior notes	131,100	127,617
6.625% Senior Notes Due 2021 [Member] | Senior Notes [Member] | Significant Other Observable Inputs (Level 2) [Member]
Long-term Borrowings:
Carrying amount of senior notes	222,240	221,840
Estimated fair value of senior notes	$ 218,700	$ 224,719