Supplementary Financial Information - Expenses and Revenue (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplementary Financial Information (unaudited)
Total revenues	$ 128,746	$ 120,769	$ 128,477	$ 131,484	$ 126,747	$ 114,531	$ 121,581	$ 120,835	$ 509,476	$ 483,694	$ 469,052
Expenses:
Compensation and employee benefits	47,787	45,244	45,099	45,787	45,283	46,755	45,994	46,684	183,917	184,716	188,886
Transaction processing	25,931	23,293	25,969	27,080	26,981	23,428	25,482	24,856	102,273	100,747	90,271
Occupancy and equipment	15,073	15,926	15,055	14,775	23,316	14,945	14,680	15,622	60,829	68,563	56,189
Telecommunications and data processing services	13,263	12,653	12,988	12,603	12,132	12,189	12,129	12,027	51,507	48,477	56,643
Restructuring charges	1	3,436		7,165					10,601		9,620
Other general and administrative	24,507	16,969	29,132	17,691	18,957	18,670	17,699	17,315	88,300	72,641	108,466
Interest expense	487	489	488	486	496	499	510	520	1,950	2,025	2,217
Total expenses	127,049	118,010	128,731	125,587	127,165	116,486	116,494	117,024
Income (loss) before income tax expense (benefit)	1,697	2,759	(254)	5,897	(418)	(1,955)	5,087	3,811	10,099	6,525	(43,240)
Income tax expense (benefit)	2,577	2,530	2,781	1,520	2,000	45,012	444	(1,491)	9,408	45,965	(17,322)
Net income (loss)	$ (880)	$ 229	$ (3,035)	$ 4,377	$ (2,418)	$ (46,967)	$ 4,643	$ 5,302	$ 691	$ (39,440)	$ (25,918)
Basic (loss) income per share (in dollars per share)	$ (0.03)	$ 0.01	$ (0.09)	$ 0.13	$ (0.07)	$ (1.42)	$ 0.14	$ 0.16	$ 0.02	$ (1.19)	$ (0.79)
Diluted (loss) income per share (in dollars per share)	$ (0.03)	$ 0.01	$ (0.09)	$ 0.13	$ (0.07)	$ (1.42)	$ 0.14	$ 0.16	$ 0.02	$ (1.19)	$ (0.79)
Basic weighted average number of common shares outstanding (in shares)	33,003	33,002	33,035	32,890	32,855	33,105	33,125	32,949	33,003	33,009	32,906
Diluted weighted average number of common shares outstanding (in shares)	33,003	34,421	33,035	33,993	32,855	33,105	34,222	34,130	34,407	33,009	32,906