Earnings Per Share - Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income/(loss) from continuing operations applicable to Piper Sandler Companies	$ (14,727)	$ 19,561
Net loss from discontinued operations	0	(139)
Net income/(loss) applicable to Piper Sandler Companies	(14,727)	19,422
Earnings allocated to participating securities	0	(1,587)
Net income/(loss) applicable to Piper Sandler Companies' common shareholders	$ (14,727)	$ 17,835
Shares for basic and diluted calculations:
Average shares used in basic computation (in shares)	13,796,000	13,204,000
Average shares used in diluted computation (in shares)	14,411,000	13,530,000
Earnings/(loss) per basic common share:
Income/(loss) from continuing operations (in dollars per share)	$ (1.07)	$ 1.36
Loss from discontinued operations (in dollars per share)	0	(0.01)
Earnings/(loss) per basic common share (in dollars per share)	(1.07)	1.35
Earnings/(loss) per diluted common share:
Income/(loss) from continuing operations (in dollars per share)	(1.07)	1.33
Loss from discontinued operations (in dollars per share)	0	(0.01)
Earnings/(loss) per diluted common share (in dollars per share)	$ (1.07)	$ 1.32
Weighted average participating shares outstanding (in shares)		1,130,844
Shares excluded from diluted EPS (in shares)		533,207
Restricted stock units
Shares for basic and diluted calculations:
Dilutive impact of securities (in shares)	106,000	205,000
Non-participating restricted shares
Shares for basic and diluted calculations:
Dilutive impact of securities (in shares)	509,000	121,000
Stock options and restricted shares
Earnings/(loss) per diluted common share:
Shares excluded from diluted EPS (in shares)	2,800,000