Discontinued Operations and Assets and Liabilities Held-for-Sale - Comprehensive Income or Loss (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other comprehensive income (loss), net of tax:
Net income	$ (6,284)	$ (1,857)	$ 2,729	$ (11,424)
Other comprehensive income (loss):
Unrealized gain (loss) on securities, net of deferred income tax and reclassification adjustments	(387)	954	(6,286)	1,484
Foreign currency translation	6	31	32	57
Total other comprehensive income (loss), net of tax	(381)	985	(6,254)	1,541
Comprehensive loss	(6,665)	(872)	(3,525)	(9,883)
Comprehensive (income) loss attributable to noncontrolling interests	1,645	(1,043)	(1,150)	(1,676)
Comprehensive loss attributable to PICO Holdings, Inc.	$ (5,020)	$ (1,915)	$ (4,675)	$ (11,559)
Net income (loss) per common share – basic and diluted:
Income (loss) from continuing operations (dollars per share)	$ (0.13)	$ (0.20)	$ 0.39	$ (0.60)
Income (loss) from discontinued operations (dollars per share)	(0.07)	0.07	(0.32)	0.03
Net income (loss) per common share – basic and diluted (dollars per share)	$ (0.20)	$ (0.13)	$ 0.07	$ (0.57)
Weighted average shares outstanding (number of shares)	23,138	23,068	23,112	23,049
Discontinued Operations, Held-for-sale
Other comprehensive income (loss), net of tax:
Net income					$ (13,029)	$ (80,879)	$ (59,605)
Other comprehensive income (loss):
Unrealized gain (loss) on securities, net of deferred income tax and reclassification adjustments					1,671	292	(2,093)
Foreign currency translation					29	(48)	6,578
Total other comprehensive income (loss), net of tax					1,700	244	4,485
Comprehensive loss					(11,329)	(80,635)	(55,120)
Comprehensive (income) loss attributable to noncontrolling interests					(8,836)	(979)	7,180
Comprehensive loss attributable to PICO Holdings, Inc.					$ (20,165)	$ (81,614)	$ (47,940)
Net income (loss) per common share – basic and diluted:
Income (loss) from continuing operations (dollars per share)					$ (1.09)	$ (1.76)	$ (1.34)
Income (loss) from discontinued operations (dollars per share)					0.14	(1.80)	(0.96)
Net income (loss) per common share – basic and diluted (dollars per share)					$ (0.95)	$ (3.56)	$ (2.30)
Weighted average shares outstanding (number of shares)					23,054	23,014	22,802