Consideration Transferred, Identifiable Net Assets Acquired and Goodwill Recognized (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair value of consideration transferred
Fair value of Company shares issued, net of equity issuance costs	$ 45,033
Cash consideration for outstanding shares	24,858
Total fair value of consideration transferred	69,891
Identifiable assets acquired
Cash and cash equivalents	51,013
Investment securities, available-for-sale	123,701
Loans receivable	387,185
Core deposit intangible	5,739
Accrued income and other assets	39,325
Total identifiable assets acquired	606,963
Liabilities assumed
Deposits	550,177
Federal Home Loan Bank advances and other borrowed funds	5,467
Accrued expenses and other liabilities	5,034
Total liabilities assumed	560,678
Total identifiable net assets	46,285
Goodwill recognized	23,606	0	0
Wheatland Bankshares
Fair value of consideration transferred
Fair value of Company shares issued, net of equity issuance costs	28,290
Cash consideration for outstanding shares	11,025
Total fair value of consideration transferred	39,315
Identifiable assets acquired
Cash and cash equivalents	23,148
Investment securities, available-for-sale	75,643
Loans receivable	171,199
Core deposit intangible	2,079
Accrued income and other assets	15,063
Total identifiable assets acquired	287,132
Liabilities assumed
Deposits	255,197
Federal Home Loan Bank advances and other borrowed funds	5,467
Accrued expenses and other liabilities	562
Total liabilities assumed	261,226
Total identifiable net assets	25,906
Goodwill recognized	13,409
North Cascades Bancshares
Fair value of consideration transferred
Fair value of Company shares issued, net of equity issuance costs	16,743
Cash consideration for outstanding shares	13,833
Total fair value of consideration transferred	30,576
Identifiable assets acquired
Cash and cash equivalents	27,865
Investment securities, available-for-sale	48,058
Loans receivable	215,986
Core deposit intangible	3,660
Accrued income and other assets	24,262
Total identifiable assets acquired	319,831
Liabilities assumed
Deposits	294,980
Federal Home Loan Bank advances and other borrowed funds	0
Accrued expenses and other liabilities	4,472
Total liabilities assumed	299,452
Total identifiable net assets	20,379
Goodwill recognized	$ 10,197