Parent Company Only (Details 2) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net income	$ 73,917	$ 88,141	$ 77,969	$ 82,839	$ 71,891	$ 85,552	$ 71,436	$ 71,945	$ 322,866	$ 300,824	$ 197,063
Adjustments to reconcile net income to net cash used in operating activities:
Increase in other assets									(143,617)	(123,542)	(105,720)
Increase (decrease) in other liabilities									87,884	(5,026)	10,289
Net cash (used in)/provided by operating activities									(240,268)	(679,715)	132,161
Investing Activities
Net cash used in investing activities									(2,276,077)	(1,992,746)	(3,215,745)
Financing Activities
Preferred dividends paid									(9,750)	(9,750)	(9,750)
Net other borrowings									(1,500,000)	1,100,000	800,000
Net cash provided by financing activities									3,861,863	2,846,935	3,149,823
Net increase (decrease) in cash and cash equivalents									1,345,518	174,474	66,239
Cash and cash equivalents at beginning of period				3,080,065				2,905,591	3,080,065	2,905,591	2,839,352
Cash and cash equivalents at end of period	4,425,583				3,080,065				4,425,583	3,080,065	2,905,591
Texas Capital Bancshares, Inc.
Operating activities
Net income									320,682	298,640	193,423
Adjustments to reconcile net income to net cash used in operating activities:
Equity in undistributed income of subsidiary									(323,783)	(300,758)	(194,118)
Amortization									101	101	101
Increase in other assets									(1,187)	(1,152)	(739)
Increase (decrease) in other liabilities									297	227	(40)
Net cash (used in)/provided by operating activities									(3,890)	(2,942)	(1,373)
Investing Activities
Net increase in loans held for investment									(3,000)	0	(7,500)
Investments in and advances to subsidiaries									0	(40,000)	(55,000)
Net cash used in investing activities									(3,000)	(40,000)	(62,500)
Financing Activities
Costs from issuance of stock related to stock-based awards and warrants									(1,459)	(2,382)	(2,241)
Preferred dividends paid									(9,750)	(9,750)	(9,750)
Net cash provided by financing activities									(11,209)	(12,132)	(11,991)
Net increase (decrease) in cash and cash equivalents									(18,099)	(55,074)	(75,864)
Cash and cash equivalents at beginning of period				$ 89,561				$ 144,635	89,561	144,635	220,499
Cash and cash equivalents at end of period	$ 71,462				$ 89,561				$ 71,462	$ 89,561	$ 144,635