Condensed Financial Information of Parent Company (Schedule of Statements of Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 24,033us-gaap_NetIncomeLoss	$ 23,497us-gaap_NetIncomeLoss	$ 23,303us-gaap_NetIncomeLoss
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Net cash provided by operating activities	34,843	28,886	35,328
Cash flows from investing activities:
Net increase in securities	(54,054)	(104,351)	(114,646)
Net decrease in loans	(16,954)	34,378	(19,165)
Purchases of premises and equipment, net	(6,291)	(4,857)	(3,099)
Net cash (used in) provided by investing activities	(100,949)	24,901	(65,207)
Cash flows from financing activities:
Net increase (decrease) in accounts and drafts payable	111,475	21,192	(72,440)
Cash dividends paid	(9,337)us-gaap_PaymentsOfDividendsCommonStock	(8,510)us-gaap_PaymentsOfDividendsCommonStock	(7,361)us-gaap_PaymentsOfDividendsCommonStock
Purchase of common shares of treasury	(1,848)
Other financing activities	(814)	(1,083)	(534)
Net cash (used in) provided by financing activities	135,179	30,387	(64,995)
Net increase (decrease) in cash and cash equivalents	69,073	84,174	(94,874)
Cash and cash equivalents at beginning of year	225,262	141,088	235,962
Cash and cash equivalents at end of year	294,335	225,262	141,088
Parent Company [Member]
Cash flows from operating activities:
Net income	24,033	23,497	23,303
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity in undistributed income of subsidiaries	(7,164)	(7,530)	(7,523)
Net change in other assets	(44,879)	(8,420)	(3,338)
Net change in other liabilities	534	(2,729)	5,603
Amortization of stock-based awards	1,250	1,177	1,201
Other, net	13,487	(4,180)	(2,673)
Net cash provided by operating activities	(12,739)	1,815	16,573
Cash flows from investing activities:
Net increase in securities	(35,128)	(15,385)	(7,697)
Net decrease in loans	9,358	31,619	16,319
Purchases of premises and equipment, net	(8,941)	(4,050)	(3,555)
Net cash (used in) provided by investing activities	(34,711)	12,184	5,067
Cash flows from financing activities:
Net increase (decrease) in accounts and drafts payable	111,405	21,192	(72,440)
Cash dividends paid	(9,337)	(8,510)	(7,361)
Other financing activities	(1,869)	(513)	(2,454)
Net cash (used in) provided by financing activities	100,199	12,169	(82,255)
Net increase (decrease) in cash and cash equivalents	52,749	26,168	(60,615)
Cash and cash equivalents at beginning of year	87,582	61,414	122,029
Cash and cash equivalents at end of year	$ 140,331	$ 87,582	$ 61,414

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585