Borrowings - Contractual Maturities of Long-Term Advances (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Long-term Debt, Fiscal Year Maturity [Abstract]
2016	$ 0	$ 85,000
2017	205,000	180,000
2018	55,000	55,000
Total long-term borrowings	$ 260,000	$ 320,000
2016, rate	0.00%	0.59%
2017, rate	1.18%	1.21%
2018, rate	1.61%	1.61%