Securities Financing Including Redeemable Preferred Stocks - Summary of Redeemable Preferred Stock (Detail) - Series E Redeemable Preferred Stock [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Stockholders Equity [Line Items]
Beginning balance	$ 145,029
Beginning balance, shares	139,768
Accretion relating to liquidation preference on preferred stock	$ 1,124
Accretion for discount and issuance costs on preferred stock	475
Accumulated dividends	5,536	$ 7,350
Ending balance	$ 152,164
Ending balance, shares	139,768