Recently Adopted Accounting Standards and Recently Issued Accounting Pronouncements - Additional Information (Detail) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) Asset
Summary Of Significant Accounting Policies [Line Items]
Prepaid income taxes				$ 8,600
Number of assets transferred | Asset				2
Increase (decrease) in net cash from operating activities		$ (3,560)	$ (10,899)
ASU 2016-01 and 2018-03 [Member]
Summary Of Significant Accounting Policies [Line Items]
Impact on remeasurement of equity investments recorded within other long term assets	$ 1,600
Impact on remeasurement of equity investments per share before taxes recorded within other income | $ / shares	$ 0.09
ASU 2016-16, as Amended [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative-effect adjustment to retained earnings	$ 1,900
ASU 2016-18 [Member]
Summary Of Significant Accounting Policies [Line Items]
Increase (decrease) in net cash from operating activities			$ (14,400)
ASU 2017-01 [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets Acquired Not Meeting The Definition of a Business		$ 1,900