FIRST BANCORP. (Holding Company Only) Financial Information - Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
ASSETS
Cash and due from banks	$ 726,779	$ 289,591	$ 518,835
Money market investments	10,415	10,094	10,108
Investment securities available for sale, at market:
Other investment securities	1,401,748	1,542,530
Carrying Value Of Other Equity Security	2,200	2,200
Loans Receivable, net	8,673,920	8,731,276
Other assets	462,861	476,430
Total assets	12,173,648	11,922,455
Liabilities:
Other borrowings	208,639	216,187
Accounts payable and other liabilities	130,367	118,820
Total liabilities	10,319,897	10,136,212
Stockholders Equity	1,853,751	1,786,243	$ 1,799,886
Total liabilities and stockholders' equity	12,173,648	11,922,455
Holding Company [Member]
ASSETS
Cash and due from banks	19,091	29,393
Money market investments	6,111	6,111
Investment securities available for sale, at market:
Carrying Value Of Other Equity Security	285	285
Loans Receivable, net	199	227
Other assets	6,672	3,791
Total assets	2,063,325	2,003,449
Liabilities:
Other borrowings	208,639	216,187
Accounts payable and other liabilities	935	1,019
Total liabilities	209,574	217,206
Stockholders Equity	1,853,751	1,786,243
Total liabilities and stockholders' equity	2,063,325	2,003,449
Holding Company [Member] | Investment In Banking Subsidiary [Member]
Investment securities available for sale, at market:
Equity Method Investments	2,012,945	1,946,211
Holding Company [Member] | Non Banking Subsidiary [Member]
Investment securities available for sale, at market:
Equity Method Investments	11,759	10,941
Holding Company [Member] | Statutory Trust One [Member]
Investment securities available for sale, at market:
Equity Method Investments	2,702	2,929
Holding Company [Member] | Statutory Trust Two [Member]
Investment securities available for sale, at market:
Equity Method Investments	$ 3,561	$ 3,561