Investment Securities - HTM (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
HTM Securities
Net Carrying Amount (Amortized Cost)	$ 411,196	$ 509,980
Gross Unrealized Holdings Gains	3,121	2,833
Gross Unrealized Holdings Losses	(5,875)	(8,648)
Fair Value	408,442	504,165
HTM preferred equity interests
Less than one year	129,282
One to three years	261,684
Thereafter	20,230
Total	411,196	509,980
Preferred Equity Investment
HTM Securities
Net Carrying Amount (Amortized Cost)	20,230	19,873
Gross Unrealized Holdings Gains	675	727
Fair Value	20,905	20,600
HTM preferred equity interests
Thereafter	20,230
Total	20,230	19,873
CMBS
HTM Securities
Net Carrying Amount (Amortized Cost)	390,966	490,107
Gross Unrealized Holdings Gains	2,446	2,106
Gross Unrealized Holdings Losses	(5,875)	(8,648)
Fair Value	387,537	483,565
HTM preferred equity interests
Less than one year	129,282
One to three years	261,684
Total	$ 390,966	$ 490,107