Parent Company Condensed Financial Information - Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Information [Line Items]
Net Income	$ 67,081	$ 57,910	$ 50,539
Tax benefit from stock-based compensation	(53)	(16)	(96)
Net Cash Provided by Operating Activities	60,584	78,103	86,076
Net Cash Used in Investing Activities	(405,737)	(437,048)	(309,683)
Cash dividends paid to common shareholders	(24,487)	(20,203)	(18,137)
Tax benefit from stock-based compensation	53	16	96
Net Cash Provided by (Used in) Financing Activities	334,972	360,169	(5,748)
Net increase (decrease) in cash	(10,181)	1,224	(229,355)
Cash and cash equivalents at beginning of year	109,580	108,356	337,711
Cash and Cash Equivalents at End of Year	99,399	109,580	108,356
Parent Company
Condensed Financial Information [Line Items]
Net Income	67,081	57,910	50,539
Equity in undistributed (earnings) losses of subsidiaries	5,440	(14,250)	(29,785)
Tax benefit from stock-based compensation	(53)	(16)	(96)
Other	3,059	(106)	121
Net Cash Provided by Operating Activities	75,527	43,538	20,779
Net investments in subsidiaries	(38,404)	0	0
Acquisitions	(29,510)	0	0
Net Cash Used in Investing Activities	(67,914)	0	0
Repayment of junior subordinated debt	(8,500)	0	0
(Purchase) Sale of treasury shares, net	(112)	(163)	(88)
Cash dividends paid to common shareholders	(24,487)	(20,215)	(18,137)
Tax benefit from stock-based compensation	53	16	96
Net Cash Provided by (Used in) Financing Activities	(33,046)	(20,362)	(18,129)
Net increase (decrease) in cash	(25,433)	23,176	2,650
Cash and cash equivalents at beginning of year	38,028	14,852	12,202
Cash and Cash Equivalents at End of Year	$ 12,595	$ 38,028	$ 14,852