Accounting Policies and Basis of Presentation Accounting Policies and Basis of Presentation (Recently Adopted Accounting Standards) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Apr. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Oct. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of shares authorized to be repurchased (in shares)				800,000
Stock repurchased during period (in shares)		243,000
Stock repurchased during period		$ 100,700
Stock repurchased during period (in USD per share)		$ 414.58
Total number of shares repurchase (in shares)		425,000
Operating lease assets		$ 70,815
Present value of lease liabilities		$ 72,315
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets			$ 70,700
Present value of lease liabilities			71,800
Right-of-use asset previously classified as capital lease			9,100
Liability previously classified as capital lease			8,300
Accounting Standards Update 2016-02 | HomeBancorp Inc.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Present value of lease liabilities			$ 1,100
Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock repurchased during period (in shares)	63,400
Stock repurchased during period	$ 27,400
Stock repurchased during period (in USD per share)	$ 432.78