Loans - Average Recorded Investment and Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	$ 150,291	$ 155,333	$ 217,263
Interest Income Recognized	4,646	5,010	5,945
Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	24,435	26,863	29,059
Interest Income Recognized	728	812	996
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	93,553	95,771	131,199
Interest Income Recognized	2,914	3,035	3,198
Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	77,154	74,256	110,447
Interest Income Recognized	2,380	2,488	2,946
Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	16,399	21,515	20,752
Interest Income Recognized	534	547	252
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	28,451	30,485	55,814
Interest Income Recognized	893	1,114	1,686
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	3,852	2,214	1,191
Interest Income Recognized	111	49	65
Consumer [Member] | Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	3,852	2,214	1,191
Interest Income Recognized	$ 111	$ 49	$ 65