Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands						6 Months Ended
	Aug. 07, 2018	Mar. 31, 2018	Mar. 23, 2018	May 09, 2016	Aug. 05, 2015	Jun. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Liquidation preference value				$ 137,500
Carrying Amount						$ 132,097	$ 132,097
Number of shares authorized to be repurchased						1,137,500
Stock Repurchased During Period, Value						$ 30,670
Stock Repurchased During Period, Average Cost Per Share						$ 76.67
Shares authorized to be repurchased						1,073,500
Series B Preferred Stock
Class of Stock [Line Items]
Ownership per share					6.625%
Liquidation preference value					$ 80,000
Carrying Amount						$ 76,812	76,812
Series C Preferred Stock
Class of Stock [Line Items]
Ownership per share				6.60%
Liquidation preference value				$ 57,500
Carrying Amount						$ 55,285	$ 55,285
Gibraltar Private Bank & Trust Company
Class of Stock [Line Items]
Cash consideration		$ 214,700	$ 7
Gibraltar Private Bank & Trust Company | Common Stock
Class of Stock [Line Items]
Common stock issued (shares)			2,787,773
Common stock issued (in dollars per share)			$ 77.00
Number of shares issued per share acquired			$ 1.9749
Subsequent Event
Class of Stock [Line Items]
Treasury stock acquired (shares)	363,210
Treasury stock acquired	$ 30,400
Common Stock
Class of Stock [Line Items]
Common stock repurchases (in shares)						(400,000)
Stock Repurchased During Period, Value						$ 400
Stock repurchased during period shares, approved by Board						335,000