Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Allowance for credit losses	$ 790		$ 794
Amounts pledged	644,359		438,385
Securities purchased under agreements to resell, fair value	3,617		24,006
Accumulated amortization	23,735		24,826
Accumulated allowance	7,445		6,784
Net accumulated depreciation	86,502		84,073
Unamortized debt issuance expense	1,104		648
Deferred tax assets, gross	$ 61,296		$ 59,062
Class A Stock [Member]
Common stock, shares authorized (in shares)	50,000,000		50,000,000
Common stock, shares issued (in shares)	13,132,775		13,261,095
Common stock, shares outstanding (in shares)	13,132,775	13,182,332	13,261,095	13,259,715	13,263,532	13,238,486
Common stock, par value (dollars per share)	$ 0.001		$ 0.001
Class B Stock [Member]
Common stock, shares authorized (in shares)	99,665		99,665
Common stock, shares issued (in shares)	99,665		99,665
Common stock, shares outstanding (in shares)	99,665		99,665
Common stock, par value (dollars per share)	$ 0.001		$ 0.001