Changes in Accumulated Other Comprehensive Income (Loss) By Component (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 964,636	$ 978,373	$ 1,052,795	$ 956,816
Unrealized gains (losses) arising during period, before tax	28,946	6,653	(7,849)	17,531
Income tax effect	(7,498)	(1,730)	2,219	(4,558)
Other comprehensive income (loss) before reclassifications	21,448	4,923	(5,630)	12,973
Reclassification adjustments for (gains) losses included in net income, before tax	(1,635)	4	(4,132)	(409)
Income tax effect	397	(1)	1,047	106
Amounts reclassified from accumulated other comprehensive income (loss) to net income	(1,238)	3	(3,085)	(303)
Other comprehensive income (loss), net of income tax effect	20,210	4,926	(8,715)	12,670
Ending balance	1,007,847	991,405	1,007,847	991,405
Unrealized Gains (Losses) on Available for Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	4,614	(8,556)	14,287	(21,741)
Unrealized gains (losses) arising during period, before tax	35,315	20,755	26,217	38,572
Income tax effect	(9,182)	(5,397)	(6,816)	(10,029)
Other comprehensive income (loss) before reclassifications	26,133	15,358	19,401	28,543
Reclassification adjustments for (gains) losses included in net income, before tax	(4,353)	0	(8,328)	0
Income tax effect	1,131	0	2,165	0
Amounts reclassified from accumulated other comprehensive income (loss) to net income	(3,222)	0	(6,163)	0
Other comprehensive income (loss), net of income tax effect	22,911	15,358	13,238	28,543
Ending balance	27,525	6,802	27,525	6,802
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(34,789)	(6,363)	(15,537)	(922)
Unrealized gains (losses) arising during period, before tax	(6,369)	(14,102)	(34,066)	(21,041)
Income tax effect	1,684	3,667	9,035	5,471
Other comprehensive income (loss) before reclassifications	(4,685)	(10,435)	(25,031)	(15,570)
Reclassification adjustments for (gains) losses included in net income, before tax	2,718	4	4,196	(409)
Income tax effect	(734)	(1)	(1,118)	106
Amounts reclassified from accumulated other comprehensive income (loss) to net income	1,984	3	3,078	(303)
Other comprehensive income (loss), net of income tax effect	(2,701)	(10,432)	(21,953)	(15,873)
Ending balance	(37,490)	(16,795)	(37,490)	(16,795)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(30,175)	(14,919)	(1,250)	(22,663)
Other comprehensive income (loss), net of income tax effect	20,210	4,926	(8,715)	12,670
Ending balance	$ (9,965)	$ (9,993)	$ (9,965)	$ (9,993)