Fair Value of Assets and Liabilities - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Assets
Available for sale securities	$ 247,673	$ 303,628
Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities	247,673	303,628
Liabilities
Interest rate swap	198	390
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Available for sale securities	2,010
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities	2,010
Significant Other Observable Inputs (Level 2) [Member]
Assets
Available for sale securities	243,860	302,139
Liabilities
Interest rate swap	198	390
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities	243,860	302,139
Liabilities
Interest rate swap	198	390
Significant Unobservable Inputs (Level 3) [Member]
Assets
Available for sale securities	1,803	1,489
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities	$ 1,803	$ 1,489