Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Cardinal Financial Corporation [Member]	Bank of Georgetown [Member]	Deferred Compensation Plan [Member]	Common Stock [Member]	Common Stock [Member] Cardinal Financial Corporation [Member]	Common Stock [Member] Bank of Georgetown [Member]	Common Stock [Member] Deferred Compensation Plan [Member]	Surplus [Member]	Surplus [Member] Cardinal Financial Corporation [Member]	Surplus [Member] Bank of Georgetown [Member]	Surplus [Member] Deferred Compensation Plan [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cardinal Financial Corporation [Member]	Retained Earnings [Member] Bank of Georgetown [Member]	Retained Earnings [Member] Deferred Compensation Plan [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Cardinal Financial Corporation [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Bank of Georgetown [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Deferred Compensation Plan [Member]	Treasury Stock [Member]	Treasury Stock [Member] Cardinal Financial Corporation [Member]	Treasury Stock [Member] Bank of Georgetown [Member]	Treasury Stock [Member] Deferred Compensation Plan [Member]
Beginning Balance at Dec. 31, 2014	$ 1,656,160				$ 173,286				$ 742,960				$ 776,311				$ (35,764)				$ (633)
Beginning Balance, shares at Dec. 31, 2014					69,314,407
Net income	137,959				$ 0				0				137,959				0				0
Other comprehensive income, net of tax	(2,448)				0				0				0				(2,448)				0
Total comprehensive income, net of tax	135,511
Stock based compensation expense	2,484				0				2,484				0				0				0
Purchase of treasury stock	(1)				0				0				0				0				(1)
Distribution of treasury stock for deferred compensation plan				$ 1				$ 0				$ 0				$ 0				$ 0				$ 1
Issuance of treasury stock, shares								0																24
Cash dividends	(89,667)				0				0				(89,667)				0				0
Grant of restricted stock	0				$ 132				(132)				0				0				0
Grant of restricted stock, shares					53,071
Forfeiture of restricted stock	0				$ 0				187				0				0				(187)
Common stock options exercised	$ 8,147				$ 649				7,498				0				0				0
Common stock options exercised, shares	259,454				259,454
Ending Balance at Dec. 31, 2015	$ 1,712,635				$ 174,067				752,997				824,603				(38,212)				(820)
Ending Balance, shares at Dec. 31, 2015					69,626,932
Net income	147,083				$ 0				0				147,083				0				0
Other comprehensive income, net of tax	(6,505)				0				0				0				(6,505)				0
Total comprehensive income, net of tax	140,578
Stock based compensation expense	2,817				0				2,817				0				0				0
Issuance of common stock (4,330,000 shares)	199,916				$ 10,825				189,091				0				0				0
Acquisition, Values			$ 264,495				$ 16,319				$ 248,176				$ 0				$ 0				$ 0
Issuance of common stock (4,330,000 shares), shares					4,330,000
Acquisition, Shares							6,527,746
Purchase of treasury stock	(1)				$ 0				0				0				0				(1)
Distribution of treasury stock for deferred compensation plan	52			1	$ 0			$ 0	0			0	0			0	0			0	$ 52			$ 1
Issuance of treasury stock, shares					0			0													1,500			28
Cash dividends	(98,696)				$ 0				0				(98,696)				0				$ 0
Grant of restricted stock	0				$ 161				(161)				0				0				0
Grant of restricted stock, shares					64,092
Forfeiture of restricted stock	0				$ 0				207				0				0				(207)
Common stock options exercised	$ 13,950				$ 1,299				12,651				0				0				0
Common stock options exercised, shares	519,482				519,482
Ending Balance at Dec. 31, 2016	$ 2,235,747				$ 202,671				1,205,778				872,990				(44,717)				(975)
Ending Balance, shares at Dec. 31, 2016					81,068,252
Net income	150,581				$ 0				0				150,581				0				0
Other comprehensive income, net of tax	2,692				0				0				0				2,692				0
Total comprehensive income, net of tax	153,273
Stock based compensation expense	3,555				0				3,555				0				0				0
Acquisition, Values		$ 975,254				$ 59,226				$ 916,028				$ 0				$ 0				$ 0
Acquisition, Shares						23,690,589
Purchase of treasury stock	(1)				0				0				0				0				(1)
Distribution of treasury stock for deferred compensation plan				$ 1				$ 0				$ 0				$ 0				$ 0				$ 1
Issuance of treasury stock, shares								0																31
Cash dividends	(131,755)				0				0				(131,755)				0				0
Grant of restricted stock	0				$ 225				(225)				0				0				0
Grant of restricted stock, shares					90,075
Forfeiture of restricted stock	0				$ 0				38				0				0				(38)
Common stock options exercised	$ 4,456				$ 553				3,903				0				0				0
Common stock options exercised, shares	220,905				220,905
Ending Balance at Dec. 31, 2017	$ 3,240,530				$ 262,675				$ 2,129,077				$ 891,816				$ (42,025)				$ (1,013)
Ending Balance, shares at Dec. 31, 2017					105,069,821