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	6 Months Ended
	Aug. 02, 2019	Jun. 30, 2019	Jun. 30, 2019	Apr. 30, 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		800,000
Stock repurchased during period (in shares)		205,500	448,500
Stock repurchased during period		$ 89,800	$ 190,500
Stock repurchased during period (in USD per share)		$ 436.81	$ 424.77
Total number of shares repurchase (in shares)		630,500	630,500
Operating lease assets		$ 81,534	$ 81,534
Present value of lease liabilities		$ 80,562	$ 80,562
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)	69,600
Stock repurchased during period	$ 31,700
Stock repurchased during period (in USD per share)	$ 455.94