Parent Company Financial Information (Statements of Cash Flows) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows from Operating Activities:
Net income	$ 12,802	$ 10,995	$ 10,333	$ 11,225	$ 9,148	$ 11,142	$ 6,982	$ 10,928	$ 45,355	$ 38,200	$ 44,422
Adjustments to reconcile net income to net cash provided by operating activities:
Share based compensation expense									1,979	1,452	1,688
Net change in other liabilities									(6,267)	20,166	(5,965)
Other-net									4,628	(4,997)	13,046
Net cash provided by operating activities									50,830	53,664	96,142
Cash Flows from Investing Activities:
Purchase of investment available-for-sale									(46,190)	0	(161,379)
Acquistion of business activity, net of cash acquired									0	0	0
Net cash used in investing activities									(291,915)	(262,337)	(233,190)
Cash Flows from Financing Activities:
Redemption of stock warrant									(22,624)	(910)	0
Proceeds from issuance of common stock									487	394	153
Tax benefit from stock options exercised									350	321	0
Repurchase of common stock									(22,624)	(910)	0
Dividends paid									(22,397)	(19,216)	(16,130)
Net cash provided by financing activities									217,750	230,463	125,069
Net increase (decrease) in cash and cash equivalents									(23,335)	21,790	(11,979)
Cash and cash equivalents at beginning of period				96,217				74,427	96,217	74,427	86,406
Cash and cash equivalents at end of period	72,882				96,217				72,882	96,217	74,427
Parent Company [Member]
Cash Flows from Operating Activities:
Net income									45,355	38,200	44,422
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed income-subsidiary									(3,494)	(19,443)	(28,574)
Share based compensation expense									1,979	1,452	1,688
Other-net									10	(261)	(43)
Net cash provided by operating activities									43,850	19,948	17,493
Cash Flows from Investing Activities:
Purchase of investment available-for-sale									(2,600)	0	0
Net cash used in investing activities									(2,600)	0	0
Cash Flows from Financing Activities:
Proceeds from issuance of common stock									487	394	153
Tax benefit from stock options exercised									350	321	0
Repurchase of common stock									(22,624)	(910)	0
Dividends paid									(22,397)	(19,216)	(16,130)
Net cash provided by financing activities									(44,184)	(19,411)	(15,977)
Net increase (decrease) in cash and cash equivalents									(2,934)	537	1,516
Cash and cash equivalents at beginning of period				$ 12,088				$ 11,551	12,088	11,551	10,035
Cash and cash equivalents at end of period	$ 9,154				$ 12,088				$ 9,154	$ 12,088	$ 11,551