Securities Available-for-Sale - Estimated Maturity Distribution of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 173,276
After one but within five years, Amortized Cost	107,005
After five but within ten years, Amortized Cost	168,698
More than ten years, Amortized Cost	49,625
Non-maturing, Amortized Cost	1,616
Amortized Cost	500,220	$ 404,977
Within one year, Fair Value	173,263
After one but within five years, Fair Value	106,782
After five but within ten years, Fair Value	168,347
More than ten years, Fair Value	49,207
Non-maturing, Fair Value	1,698
Total, Fair Value	$ 499,297	$ 404,623