Ownership, Description of Business, and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 12, 2015
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Restricted cash	$ 21,800,000	$ 21,000,000
Stock repurchase program, authorized amount				$ 50,000,000
Anti-dilutive employee stock options outstanding (in shares)	66	107	3
2020 Convertible Senior Notes
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Convertible/exchangeable debt	$ 172,500,000
Initial conversion price (in dollars per share)	$ 45.72
2020 Convertible Senior Notes | Adjusted Debt Conversion Rate Following Hedge Transactions
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Initial conversion price (in dollars per share)	$ 61.55
2021 Convertible Senior Notes
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Convertible/exchangeable debt	$ 161,000,000
Initial conversion price (in dollars per share)	$ 59.39
2021 Convertible Senior Notes | Adjusted Debt Conversion Rate Following Hedge Transactions
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Initial conversion price (in dollars per share)	$ 83.14
2022 Convertible Senior Notes
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Convertible/exchangeable debt	$ 150,000,000
Initial conversion price (in dollars per share)	$ 45.57
Exchangeable Notes
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Convertible/exchangeable debt	$ 172,500,000
Initial conversion price (in dollars per share)	$ 44.62
Exchangeable Notes | Adjusted Debt Conversion Rate Following Hedge Transactions
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Initial conversion price (in dollars per share)	$ 62.48