Loans and Allowance for Loan Losses - Investment Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Acquired loans
Allowance for loan losses on loans in consolidated VIEs	$ (9,666)	$ (10,533)	$ (11,746)	$ (13,775)	$ (14,684)	$ (16,130)
Non - PCI Loans
Acquired loans
Unpaid principal balance	2,066,751		1,624,395
Accretable discount	(37,062)		(44,629)
Loans, held-for-investment	2,029,689		1,579,766
Allowance for loan losses on loans in consolidated VIEs	(3,350)		(4,442)
Loans, held-for-investment	2,026,339		1,575,324
PCI Loans
Acquired loans
Unpaid principal balance	115,741		130,015
Non-accretable discount	(9,527)		(8,336)
Accretable discount	(19,485)	$ (20,994)	(23,749)	$ (23,839)	$ (24,221)	$ (26,978)
Loans, held-for-investment	86,729		97,930
Allowance for loan losses on loans in consolidated VIEs	(6,316)		(7,304)
Loans, held-for-investment	$ 80,413		$ 90,626