Basis of Presentation and Consolidation - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 17,155	$ 21,524	$ 48,237	$ 185,606
Preferred stock issued	0	0
Net cash proceeds from stock issuance	$ 2,024
Silver Creek [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 2,800
Ownership interest percentage held by parent and its de facto agents	52.00%
Silver Creek [Member] | Series C Preferred Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Preferred stock issued	1,400
Preferred stock price per share	$ 1.50
Net cash proceeds from stock issuance	$ 2,000
Warrants issued to purchase preferred stock, shares	1,800	1,900