Restatement of Previously Issued Unaudited and Audited Financial Statements - Effect of Restatement on Condensed Consolidated Statement of Shareholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013
Condensed Consolidated Statement of Shareholders' Equity Data
Net income	$ 1,688	$ 14,591	$ 8,122	$ 12,851	$ 8,729
Balance as of September 30, 2015	151,631	142,072	125,928	151,631	125,928	$ 115,646
Retained Earnings [Member]
Condensed Consolidated Statement of Shareholders' Equity Data
Net income		14,591		12,851	8,729
Balance as of September 30, 2015	976,776	$ 963,737	$ 949,146	976,776	$ 949,146	$ 940,449
As Previously Reported [Member]
Condensed Consolidated Statement of Shareholders' Equity Data
Balance as of September 30, 2015	157,564			157,564
As Previously Reported [Member] | Retained Earnings [Member]
Condensed Consolidated Statement of Shareholders' Equity Data
Net income				12,851
Balance as of September 30, 2015	982,709			982,709
Interest Method Adjustment [Member]
Condensed Consolidated Statement of Shareholders' Equity Data
Balance as of September 30, 2015	(5,933)			(5,933)
Interest Method Adjustment [Member] | Retained Earnings [Member]
Condensed Consolidated Statement of Shareholders' Equity Data
Net income				0
Balance as of September 30, 2015	$ (5,933)			$ (5,933)