Securities Available-for-Sale - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2015 USD ($) security	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Number of debt securities on which unrealized losses were primarily attributable to changes in interest | security	7
Carrying values of securities	$ 296,100,000	$ 289,100,000
Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized losses reclassified out of accumulated other comprehensive income into earnings	$ 0