Parent Company Financial Information - Schedule of Parent Company Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES
Net income	$ 286,502	$ 243,600	$ 195,513
Depreciation and amortization	62,803	56,258	53,116
Amortization of debt issuance costs	131
Equity based compensation	15,120	14,850	11,074
Net tax benefit related to equity compensation plans	345	766	2,364
Changes in other assets and liabilities, net	(128,091)	(112,563)	(18,903)
Net cash provided by operating activities	373,598	339,933	295,696
INVESTING ACTIVITIES
Net cash used in investing activities	(4,491,087)	(2,985,161)	(1,746,545)
FINANCING ACTIVITIES
Cash dividends paid	(60,281)	(59,436)	(58,279)
Proceeds from short-term debt	15,000
Repayment of short-term debt	(15,000)
Proceeds from long-term debt	200,000
Payment of debt issuance costs	(2,250)
Purchases of treasury stock	(63,766)	(4,496)	(76,507)
Net cash provided by financing activities	5,945,885	2,640,277	1,408,708
Cash and cash equivalents at beginning of period	1,669,170
Cash and cash equivalents at end of period	3,497,566	1,669,170
Parent Company [Member]
OPERATING ACTIVITIES
Net income	286,502	243,600	195,513
Equity in earnings of subsidiaries	(301,415)	(270,747)	(206,175)
Dividends received from subsidiaries	78,360	56,500	47,250
Depreciation and amortization	15	(78)	486
Amortization of debt issuance costs	131
Equity based compensation	15,120	14,850	11,073
Net tax benefit related to equity compensation plans	345	766	2,364
Changes in other assets and liabilities, net	(2,069)	(7,864)	(5,994)
Net cash provided by operating activities	76,989	37,027	44,517
INVESTING ACTIVITIES
Net capital investment in subsidiaries	(96,678)	(331)	(17,961)
Net (increase) decrease in investment securities	(29,648)	21	1,062
Net cash used in investing activities	(126,326)	(310)	(16,899)
FINANCING ACTIVITIES
Cash dividends paid	(60,281)	(59,436)	(58,279)
Proceeds from short-term debt	15,000
Repayment of short-term debt	(15,000)
Proceeds from long-term debt	200,000
Payment of debt issuance costs	(2,250)
Proceeds from exercise of stock options and sales of treasury stock	5,186	4,637	12,318
Purchases of treasury stock	(63,766)	(4,496)	(76,507)
Net cash provided by financing activities	78,889	(59,295)	(122,468)
Net increase (decrease) in cash	29,552	(22,578)	(94,850)
Cash and cash equivalents at beginning of period	143,193	165,771	260,621
Cash and cash equivalents at end of period	$ 172,745	$ 143,193	$ 165,771