Earnings Per Share - Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ 12,555	$ 5,862	$ 32,116	$ 16,480
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(2,166)	364	(2,305)	349
Net Income (Loss) Attributable to Parent	10,389	6,226	29,811	16,829
Earnings allocated to participating securities	(238)	(704)	(1,924)	(4,634)
Net income applicable to Piper Jaffray Companies' common shareholders	$ 10,151	$ 5,522	$ 27,887	$ 12,195
Shares for basic and diluted calculations
Average shares used in basic computation	13,588,000	13,303,000	13,397,000	13,200,000
Average shares used in diluted computation	14,024,000	13,438,000	13,778,000	13,411,000
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.90	$ 0.40	$ 2.24	$ 0.88
Earnings per common share
Basic	0.75	0.43	2.08	0.91
Diluted	0.72	0.43	2.02	0.94
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	(0.15)	0.03	(0.16)	0.03
Income (Loss) from Continuing Operations, Per Diluted Share	0.87	0.40	2.18	0.91
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	$ (0.15)	$ 0.03	$ (0.16)	$ 0.03
Weighted average participating shares outstanding	403,103	1,906,364	764,963	1,997,254
Common shares excluded from diluted EPS			275,724	1,878,016
Restricted stock units
Shares for basic and diluted calculations
Dilutive impact of securities	189,000	135,000	197,000	211,000
Non-participating restricted shares
Shares for basic and diluted calculations
Dilutive impact of securities	247,000	0	184,000	0