Shareholders' Equity - Schedule of Cash Dividends Declared Per Common Share and Total Amounts Declared, Distributed and Deferred (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Stockholders Equity [Abstract]
Dividend declared per common share	$ 0.28	$ 0.22
Cash dividends declared, Amount	$ 25,769	$ 22,046
Cash dividends distributed, Amount	25,500	21,889
Cash dividends deferred, Amount	$ 269	$ 157